#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxN = 2e5+5;
ll INF = 1e9;
ll sum[maxN];
ll depth[maxN];
vector<vector<pair<ll,ll>>> adj(maxN);
vector<map<ll,ll>> mp(maxN);
ll k,n;
ll ans;
void dfs1(int s, int p) {
depth[s] = depth[p]+1;
mp[s][sum[s]] = depth[s];
for(auto [w,u] : adj[s]) {
if(u == p) continue;
sum[u] = sum[s]+w;
dfs1(u,s);
}
}
void dfs(int s, int p) {
for(auto [w,u] : adj[s]) {
if(u == p) continue;
dfs(u,s);
if(mp[u].size() > mp[s].size()) swap(mp[u],mp[s]);
for(auto pr : mp[u]) {
int cur = mp[s][k-pr.first + 2*sum[s]];
if(cur != 0) {
ans = min(ans,cur+pr.second - 2*depth[s]);
}
}
for(auto pr : mp[u]) {
if(mp[s][pr.first] == 0 || mp[s][pr.first] > pr.second) {
mp[s][pr.first] = pr.second;
}
}
}
}
ll best_path(int N, int K, int H[][2], int L[]) {
n = N;
k = K;
ans = INF;
for(int i = 0; i < N-1; i++) {
ll a = H[i][0], b = H[i][1], w = L[i];
adj[a].push_back({w,b});
adj[b].push_back({w,a});
}
sum[0] = 0;
depth[0] = 0;
dfs1(0,0);
dfs(0,0);
if(ans == INF) return -1;
return ans;
}
