#include "race.h"
#include <bits/stdc++.h>
using namespace std;
#define OPTM ios_base::sync_with_stdio(0); cin.tie(0);
#define INF int(1e9+7)
#define ln '\n'
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define us unsigned short
#define FOR(i,s,n) for (int i = s; i < n; i++)
#define FORR(i,n,s) for (int i = n; i > s; i--)
#define FORX(u, arr) for (auto u : arr)
#define PB push_back
#define in(v,x) (v.find(x) != v.end())
#define F first
#define S second
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define UM unordered_map
#define US unordered_set
#define PQ priority_queue
#define ALL(v) v.begin(), v.end()
const ll LLINF = 1e18+1;
#define int long long
struct Edge {
int F,w;
};
const int MAXN = 2e5+1, LOG = 19;
int n,k;
set<PII> v[MAXN];
int dist[MAXN], len[MAXN], p[MAXN], sz[MAXN];
UM<int,int> mp;
int jump[MAXN][LOG];
int res = LLINF;
vector<PII> add;
void pre_dfs(int s, int pa) {
FORX(u,v[s]) {
if (u.F == pa) continue;
dist[u.F] = dist[s]+1;
len[u.F] = len[s]+u.S;
p[u.F] = s;
pre_dfs(u.F,s);
}
}
void pre_lca() {
FOR(i,0,n) jump[i][0] = p[i];
FOR(j,1,LOG) {
FOR(i,0,n) {
jump[i][j] = jump[jump[i][j-1]][j-1];
}
}
}
int lca(int a, int b) {
if (dist[a] < dist[b]) swap(a,b);
FORR(j,LOG-1,-1) {
if (dist[a]-(1<<j) >= dist[b]) a = jump[a][j];
}
if (a == b) return a;
FORR(j,LOG-1,-1) {
if (jump[a][j] != jump[b][j]) {
a = jump[a][j];
b = jump[b][j];
}
}
return p[a];
}
int find_centroid(int s, int pa, int num) {
FORX(u,v[s]) {
if (u.F == pa) continue;
if (sz[u.F] > num/2) return find_centroid(u.F,s,num);
}
return s;
}
void dfs(int s, int pa) {
sz[s] = 1;
FORX(u,v[s]) {
if (u.F == pa) continue;
dfs(u.F,s);
sz[s] += sz[u.F];
}
}
void dfs1(int s, int pa, int src) {
FORX(u,v[s]) {
if (u.F == pa) continue;
int anc = lca(u.F,src);
int l = len[u.F]+len[src]-2*len[anc];
int d = dist[u.F]+dist[src]-2*dist[anc];
if (l == k) res = min(res,d);
else if (l < k && mp.count(k-l)) res = min(res, d+mp[k-l]);
add.PB({l,d});
dfs1(u.F,s,src);
if (s == src) {
FORX(y,add) {
int l = y.F, d = y.S;
if (!mp.count(l)) mp[l] = d;
else mp[l] = min(mp[l],d);
}
add.clear();
}
}
}
void decomp(int s, int pa) {
mp.clear();
dfs(s,pa);
int c = find_centroid(s,pa,sz[s]);
dfs1(c,-1,c);
vector<PII> tmp;
FORX(u,v[s]) if (u.F != pa) tmp.PB(u);
FORX(u,tmp) {
v[s].erase(u);
v[u.F].erase({s,u.S});
decomp(u.F,c);
}
}
int32_t best_path(int32_t N, int32_t K, int32_t H[][2], int32_t L[]) {
n = N; k = K;
FOR(i,0,n-1) {
v[H[i][0]].insert({H[i][1],L[i]});
v[H[i][1]].insert({H[i][0],L[i]});
}
pre_dfs(0,-1);
pre_lca();
decomp(0,-1);
return res == LLINF ? -1 : res;
}
