#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int best_path(int n, int k, int h[][2], int l[]) {
vector<vector<pair<int, int>>> adj(n);
for (int i = 0; i < n - 1; ++i) {
adj[h[i][0]].push_back({h[i][1], l[i]});
adj[h[i][1]].push_back({h[i][0], l[i]});
}
vector<set<pair<ll, int>>> at(n);
vector<pair<ll, int>> add(n);
int ans = INT32_MAX;
auto dfs = [&](auto&& self, int node, int p) -> void {
at[node].insert({0, 0});
for (pair<int, int>& c : adj[node]) {
if (c.first == p) continue;
self(self, c.first, node);
add[c.first].first += c.second;
++add[c.first].second;
if (at[node].size() < at[c.first].size()) {
swap(at[node], at[c.first]);
swap(add[node], add[c.first]);
}
for (pair<ll, int> i : at[c.first]) {
ll other = (k - (i.first + add[c.first].first)) - add[node].first;
auto it = at[node].lower_bound({other, INT32_MIN});
if (it != at[node].end() && it->first == other) {
ans = min(ans, i.second + it->second + add[c.first].second + add[node].second);
}
}
for (pair<ll, int> i : at[c.first]) {
at[node].insert({i.first + add[c.first].first - add[node].first, i.second + add[c.first].second - add[node].second});
}
at[c.first].clear();
}
};
dfs(dfs, 0, -1);
return (ans == INT32_MAX ? -1 : ans);
}
/*int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int h[][2] = {{0, 1}, {1, 2}, {1, 3}};
int l[] = {1, 2, 4};
cout << best_path(4, 3, h, l) << '\n';
int h2[][2] = {{0, 1}, {1, 2}};
int l2[] = {1, 1};
cout << best_path(3, 3, h2, l2) << '\n';
int h3[][2] = {{0, 1}, {0, 2}, {2, 3}, {3, 4}, {4, 5}, {0, 6}, {6, 7}, {6, 8}, {8, 9}, {8, 10}};
int l3[] = {3, 4, 5, 4, 6, 3, 2, 5, 6, 7};
cout << best_path(11, 12, h3, l3) << '\n';
return 0;
}*/
