#include <bits/stdc++.h>
//#include "race.h"
using namespace std;
#define sp ' '
#define endl '\n'
#define st first
#define nd second
#define sz(x) ((long long int)x.size())
#define pb push_back
#define pob pop_back
#define mp make_pair
#define forn(YY, yy) for(long long int yy = 0; yy < YY; ++yy)
#define prn(XX) cout << XX << '\n'
#define prs(XX) cout << XX << " "
#define TEST cout << "TEST\n";
typedef long long int ll;
typedef unsigned long long int ull;
typedef vector<ll> vll;
typedef vector<vector<ll> > vvll;
typedef pair<ll, ll> pll;
typedef vector<pll> vpll;
typedef vector<vpll> vvpll;
const long long int MOD = 1e9 + 7;
const long long int INF = 2e9 + 13;
const long long int mINF = -2e9 - 13;
const double PI = acos(-1.0);
const double EPS = 1e-9;
ll mx(ll x, ll y){ return (x>y?x:y); }
ll mn(ll x, ll y){ return (x<y?x:y); }
void max_self(ll &x, ll y){ x = mx(x, y); }
void min_self(ll &x, ll y){ x = mn(x, y); }
void add(ll &x, ll y){ x += (y%MOD); x %= MOD; }
void mul(ll &x, ll y){ x%=MOD; x *= (y%MOD); x %= MOD; }
ll us(ll n, ll x, ll m){
if(x == 0) return 1;
ll a = us(n, x>>1, m);
return (((a*a)%m)*(x&1?n:1))%m;
}
vvpll AdjList;
vll dep;
vector<set<pll>> s;
ll n, k, res = INF;
void dfs(ll u, ll par, ll cur){
forn(sz(AdjList[u]), i){
ll v = AdjList[u][i].st, w = AdjList[u][i].nd;
if(v == par) continue;
dep[v] = dep[u]+1;
dfs(v, u, cur + w);
auto itr = s[v].lower_bound(mp(cur+k, -1));
if(itr != s[v].end() and (*itr).st == cur+k){
res = mn(res, (*itr).nd - dep[u]);
//cout << "Node " << u << " nun altinda benden" << cur+k << " uzaklikta var.\n";
}
if(sz(s[v]) > sz(s[u])){ swap(s[v], s[u]); }
for(itr = s[v].begin(); itr != s[v].end(); ++itr){
pll p = *itr;
auto it = s[u].lower_bound(mp(k+2*cur-p.st, -1));
if(it != s[u].end() and (it->st) == k+2*cur-p.st){
res = mn(res, (it->nd)+p.nd-2*dep[u]);
//cout << "Ben " << u << "yum. Iki nodeum {" << itr->st << sp << itr->nd << "} {" << it->st << sp << it->nd << "}\n";
}
}
for(auto itr = s[v].begin(); itr != s[v].end(); ++itr) s[u].insert(*itr);
}
auto itr = s[u].lower_bound(mp(cur+k, -1));
if(itr != s[u].end() and (*itr).st == cur+k) res = mn(res, (*itr).nd);
s[u].insert(mp(cur, dep[u]));
return;
}
int best_path(int N, int K, int H[][2], int L[]){
n = N, k = K;
AdjList.resize(n);
dep.resize(n);
s.resize(n);
forn(n-1, i){
AdjList[H[i][0]].pb(mp(H[i][1], L[i]));
AdjList[H[i][1]].pb(mp(H[i][0], L[i]));
}
dfs(0, -1, 0);
return (res>=2e9?-1:res);
}
/*int main(int argc, char** argv){
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
//freopen("race.gir", "r", stdin);
//freopen("race.cik", "w", stdout);
cin >> n >> k;
AdjList.resize(n);
dep.resize(n);
s.resize(n);
forn(n-1, i){
ll u, v, w;
cin >> u >> v >> w;
AdjList[u].pb(mp(v, w));
AdjList[v].pb(mp(u, w));
}
dfs(0, -1, 0);
cout << ((res>=2e9)?-1:res) << endl;
return 0;
}*/
//cikisir
