#include<bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
const int SIZE = 200000;
int n, k, ans = INT_MAX;
vector<pii> G[SIZE];
pii dis[SIZE];
int BFS(int S) {
fill(dis, dis + n, make_pair(INT_MAX, INT_MAX));
queue<int> q; //len, cost
q.push(S);
dis[S] = make_pair(0, 0);
while(!q.empty()) {
int now = q.front(); q.pop();
int len = dis[now].first, cost = dis[now].second;
for(auto [X, C] : G[now]) {
if (dis[X].first == INT_MAX) {
dis[X] = make_pair(len + 1, cost + C);
q.push(X);
}
}
}
int tmp = INT_MAX;
for(int i = 0; i < n; i++)
if (dis[i].second == k)
tmp = min(tmp, dis[i].first);
return tmp;
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N, k = K;
for(int i = 0; i < N - 1; i++) {
G[H[i][0]].emplace_back(make_pair(H[i][1], L[i]));
G[H[i][1]].emplace_back(make_pair(H[i][0], L[i]));
}
for(int i = 0; i < N; i++)
ans = min(ans, BFS(i));
return ans == INT_MAX ? -1 : ans;
}
/*
int A[SIZE - 1][2], B[SIZE - 1];
int main() {
int a, b; cin >> a >> b;
for(int i = 0; i < a - 1; i++)
cin >> A[i][0] >> A[i][1];
for(int i = 0; i < a - 1; i++)
cin >> B[i];
cout << best_path(a, b, A, B) << '\n';
}
*/
