#include <bits/stdc++.h>
using namespace std;
int best_path(int n, int k, int edges[][2], int w[]) {
vector<vector<pair<int, int>>> g(n);
for (int i = 0; i < n - 1; i++) {
g[edges[i][0]].emplace_back(edges[i][1], w[i]);
g[edges[i][1]].emplace_back(edges[i][0], w[i]);
}
int ans = (int) 1e9;
vector<map<long long, int>> s(n);
vector<pair<long long, int>> offset(n);
function<void(int, int)> dfs = [&](int v, int p) {
s[v][0] = 0;
for (auto&x : g[v]) {
int u = x.first;
if (u == p) continue;
dfs(u, v);
offset[u].first += x.second;
offset[u].second++;
if ((int) s[v].size() < (int) s[u].size()) {
swap(s[v], s[u]);
swap(offset[v], offset[u]);
}
for (auto& now : s[u]) {
auto it = s[v].find(k - now.first - offset[v].first - offset[u].first);
if (it != s[v].end()) {
ans = min(ans, it->second + now.second + offset[v].second + offset[u].second);
}
}
for (auto& now : s[u]) {
int need = now.first + offset[u].first - offset[v].first;
if (!s[v].count(need)) s[v][need] = (int) 1e9;
s[v][need] = min(s[v][need], now.second + offset[u].second - offset[v].second);
}
}
};
dfs(0, -1);
if (ans == (int) 1e9) ans = -1;
return ans;
}
/*
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
cout << best_path(3, 3, {{0, 1}, {1, 2}}, {1, 1});
}*/
