#include "race.h"
#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 200200;
int ans = -1, d[N], K;
ll len[N];
vector<pair<int, int>> g[N];
void calc(int u,int p,ll x = 0) {
len[u] = x;
for(auto to : g[u]) if(to.first != p) {
d[to.first] = d[u] + 1;
calc(to.first, u, x + to.second);
}
}
map<ll, int> dfs(int u,int p) {
map<ll, int> own;
own[len[u]] = d[u];
for(auto to : g[u]) if(to.first != p) {
auto x = dfs(to.first, u);
if(x.size() > own.size()) {
own.swap(x);
}
for(auto it : x) {
if(own.count(K - it.first + 2 * len[u])) {
if(ans == -1) {
ans = own[K - it.first + 2 * len[u]] + it.second - 2 * d[u];
} else {
ans = min(ans, own[K - it.first + 2 * len[u]] + it.second - 2 * d[u]);
}
}
if(own.count(it.first)) {
own[it.first] = min(own[it.first], it.second);
} else {
own[it.first] = it.second;
}
}
}
return own;
}
int best_path(int n, int k, int h[][2], int l[]) {
K = k;
for(int i = 0; i < n - 1; i++) {
int u = h[i][0],v = h[i][1], w = l[i];
g[u].push_back({v, w});
g[v].push_back({u, w});
}
calc(0, -1);
dfs(0, -1);
return ans;
}
