#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]) {
if(mp[s].find(k-pr.first+2*sum[s]) != mp[s].end()) {
ans = min(ans, mp[s][k-pr.first + 2*sum[s]] + pr.second - 2*depth[s]);
}
}
for(auto pr : mp[u]) {
if(mp[s].find(pr.first) == mp[s].end()) {
mp[s].insert(pr);
}
else {
mp[s][pr.first] = min(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;
}
/*int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int N,K;
cin >> N >> K;
int H[N-1][2];
int L[N-1];
for(int i = 0; i < N-1; i++) {
int a,b;
cin >> a >> b;
H[i][0] = a;
H[i][1] = b;
}
for(int i = 0; i < N-1; i++) {
int w;
cin >> w;
L[i] = w;
}
cout << best_path(N,K,H,L) << '\n';
}*/
