#include "bits/stdc++.h"
#include "race.h"
using namespace std;
typedef long long ll;
typedef long double ld;
typedef double db;
typedef string str;
typedef pair<int,int> pi;
typedef pair<pi, int> pii;
typedef pair<ll,ll> pl;
typedef pair<db,db> pd;
typedef vector<int> vi;
typedef vector<bool> vb;
typedef vector<ll> vl;
typedef vector<db> vd;
typedef vector<str> vs;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<pd> vpd;
template<class T> using V = vector<T>;
template<class T, size_t SZ> using AR = array<T,SZ>;
#define mp make_pair
#define f first
#define s second
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend()
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pf push_front
#define pb push_back
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define For(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define Rof(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
template<class T> bool ckmin(T& a, const T& b) {
return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) {
return a < b ? a = b, 1 : 0; }
constexpr int pct(int x) { return __builtin_popcount(x); }
constexpr int bits(int x) { return 31-__builtin_clz(x); } // floor(log2(x))
ll cdiv(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll fdiv(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down
ll half(ll x) { return fdiv(x,2); }
template<class T, class U> T fstTrue(T lo, T hi, U f) {
// note: if (lo+hi)/2 is used instead of half(lo+hi) then this will loop infinitely when lo=hi
hi ++; assert(lo <= hi); // assuming f is increasing
while (lo < hi) { // find first index such that f is true
T mid = half(lo+hi);
f(mid) ? hi = mid : lo = mid+1;
}
return lo;
}
template<class T, class U> T lstTrue(T lo, T hi, U f) {
lo --; assert(lo <= hi); // assuming f is decreasing
while (lo < hi) { // find first index such that f is true
T mid = half(lo+hi+1);
f(mid) ? lo = mid : hi = mid-1;
}
return lo;
}
template<class T> void remDup(vector<T>& v) {
sort(all(v)); v.erase(unique(all(v)),end(v)); }
// INPUT
template<class A> void re(complex<A>& c);
template<class A, class B> void re(pair<A,B>& p);
template<class A> void re(vector<A>& v);
template<class A, size_t SZ> void re(array<A,SZ>& a);
template<class T> void re(T& x) { cin >> x; }
void re(db& d) { str t; re(t); d = stod(t); }
void re(ld& d) { str t; re(t); d = stold(t); }
template<class H, class... T> void re(H& h, T&... t) { re(h); re(t...); }
template<class A> void re(complex<A>& c) { A a,b; re(a,b); c = {a,b}; }
template<class A, class B> void re(pair<A,B>& p) { re(p.f,p.s); }
template<class A> void re(vector<A>& x) { trav(a,x) re(a); }
template<class A, size_t SZ> void re(array<A,SZ>& x) { trav(a,x) re(a); }
// TO_STRING
#define ts to_string
str ts(char c) { return str(1,c); }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
str ts(bool b) {
#ifdef LOCAL
return b ? "true" : "false";
#else
return ts((int)b);
#endif
}
template<class A> str ts(complex<A> c) {
stringstream ss; ss << c; return ss.str(); }
str ts(vector<bool> v) {
str res = "{"; F0R(i,sz(v)) res += char('0'+v[i]);
res += "}"; return res; }
template<size_t SZ> str ts(bitset<SZ> b) {
str res = ""; F0R(i,SZ) res += char('0'+b[i]);
return res; }
template<class A, class B> str ts(pair<A,B> p);
template<class T> str ts(T v) { // containers with begin(), end()
#ifdef LOCAL
bool fst = 1; str res = "{";
for (const auto& x: v) {
if (!fst) res += ", ";
fst = 0; res += ts(x);
}
res += "}"; return res;
#else
bool fst = 1; str res = "";
for (const auto& x: v) {
if (!fst) res += " ";
fst = 0; res += ts(x);
}
return res;
#endif
}
template<class A, class B> str ts(pair<A,B> p) {
#ifdef LOCAL
return "("+ts(p.f)+", "+ts(p.s)+")";
#else
return ts(p.f)+" "+ts(p.s);
#endif
}
// OUTPUT
template<class A> void pr(A x) { cout << ts(x); }
template<class H, class... T> void pr(const H& h, const T&... t) {
pr(h); pr(t...); }
void ps() { pr("\n"); } // print w/ spaces
template<class H, class... T> void ps(const H& h, const T&... t) {
pr(h); if (sizeof...(t)) pr(" "); ps(t...); }
// DEBUG
void DBG() { cerr << "]" << endl; }
template<class H, class... T> void DBG(H h, T... t) {
cerr << ts(h); if (sizeof...(t)) cerr << ", ";
DBG(t...); }
#ifdef LOCAL // compile with -DLOCAL, chk -> fake assert
#define dbg(...) cerr << "Line(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#define chk(...) if (!(__VA_ARGS__)) cerr << "Line(" << __LINE__ << ") -> function(" \
<< __FUNCTION__ << ") -> CHK FAILED: (" << #__VA_ARGS__ << ")" << "\n", exit(0);
#else
#define dbg(...) 0
#define chk(...) 0
#endif
int gcd(int a, int b) {if (b == 0)return a;return gcd(b, a % b);}
int max(int a,int b, int c){return max(a,max(b,c));}
int min(int a,int b, int c){return min(a,min(b,c));}
ll max(ll a,ll b, ll c){return max(a,max(b,c));}
ll min(ll a,ll b, ll c){return min(a,min(b,c));}
void dbga(int arr[], int n){vi v;For(i,n)v.pb(arr[i]);dbg(v);}
void dbga(ll arr[], int n){vi v;For(i,n)v.pb(arr[i]);dbg(v);}
// FILE I/O
void setIn(str s) { freopen(s.c_str(),"r",stdin); }
void setOut(str s) { freopen(s.c_str(),"w",stdout); }
void unsyncIO() { cin.tie(0)->sync_with_stdio(0); }
void setIO(str s = "") {
unsyncIO();
// cin.exceptions(cin.failbit);
// throws exception when do smth illegal
// ex. try to read letter into int
if (sz(s)) { setIn(s+".in"), setOut(s+".out"); } // for USACO
}
// 576743 29995400689069LL
const int MOD = 1e9+7; // 998244353;
const int MX = 2e5+5;
const ll INF = 1e18;
const ld PI = acos((ld)-1);
const int xd[4] = {1,0,-1,0}, yd[4] = {0,1,0,-1};
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
int mn=MOD, K;
template<int SZ> struct Centroid {
vpi adj[SZ];
void ae(int a,int b, int c){adj[a].pb(mp(b,c)),adj[b].pb(mp(a,c));}
bool done[SZ]; // processed as centroid yet
int N,sub[SZ],cen[SZ],lev[SZ]; // subtree size, centroid anc
int dist[32-__builtin_clz(SZ)][SZ]; // dists to all ancs
map<int,int> m, todo;
void dfs(int x, int p, int len, int len2, bool on) {
if(len>K)return;
//del when len goes over
sub[x] = 1;
if(on){
if(todo[len])ckmin(todo[len],len2);
else todo[len]=len2;
if(m[K-len])
ckmin(mn,len2+m[K-len]);
if(len==K)
ckmin(mn,len2);
}
trav(y,adj[x]) if (!done[y.f] && y.f != p)
dfs(y.f,x,len+y.s,len2+1,on), sub[x] += sub[y.f];
}
int centroid(int x) {
dfs(x,-1,0,0,0);
for (int sz = sub[x];;) {
pi mx = {0,0};
trav(y,adj[x]) if (!done[y.f] && sub[y.f] < sub[x])
ckmax(mx,{sub[y.f],y.f});
if (mx.f*2 <= sz) return x;
x = mx.s;
}
}
void genDist(int x, int p, int lev) {
dist[lev][x] = dist[lev][p]+1;
trav(y,adj[x]) if (!done[y.f] && y.f != p) genDist(y.f,x,lev); }
void gen(int CEN, int _x) { // CEN = centroid above x
int x = centroid(_x); done[x] = 1; cen[x] = CEN;
sub[x] = sub[_x]; lev[x] = (CEN == -1 ? 0 : lev[CEN]+1);
dist[lev[x]][x] = 0;
m.clear();todo.clear();//HERE
trav(y,adj[x])if(!done[y.f]){
dfs(y.f,x,y.s,1,1);
trav(z,todo){
if(m[z.f])ckmin(m[z.f],z.s);
else m[z.f]=z.s;
}
todo.clear();
}
trav(y,adj[x]) if (!done[y.f]) genDist(y.f,x,lev[x]);
trav(y,adj[x]) if (!done[y.f]) gen(x,y.f);
}
void init(int _N) { N = _N; FOR(i,1,N+1) done[i] = 0;
gen(-1,1);//changed to 0
} // start at vert 1
// void upd(int x, int y) {
// int cur = x, pre = -1;
// R0F(i,lev[x]+1) {
// ad(stor[cur],y-dist[i][x]);
// if (pre != -1) ad(STOR[pre],y-dist[i][x]);
// if (i > 0) pre = cur, cur = cen[cur];
// }
// } // call propAll() after all updates
// void propAll() { FOR(i,1,N+1) prop(stor[i]), prop(STOR[i]); }
// int query(int x) { // get value at vertex x
// int cur = x, pre = -1, ans = 0;
// R0F(i,lev[x]+1) { // if pre != -1, subtract those from
// ans += stor[cur][dist[i][x]]; // same subtree
// if (pre != -1) ans -= STOR[pre][dist[i][x]];
// if (i > 0) pre = cur, cur = cen[cur];
// }
// return ans;
// }
};
Centroid<MX> C;
int best_path(int n, int k, int h[][2], int l[]){
K=k;
For(i,n-1)C.ae(h[i][0]+1,h[i][1]+1,l[i]);
C.init(n+5);
if(mn==MOD)ps(-1);
else ps(mn);
}
/* stuff you should look for
* int overflow, array bounds
* special cases (n=1?)
* do smth instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
*/
