#include "race.h"
#include <bits/stdc++.h>
#define DEBUG 0
using namespace std;
const int INF = 1e9, N = 2e5+10;
int dep[N], ans = INF;
long long qs[N];
vector<pair<int,int>> G[N];
map<long long, int> mp[N];
void dfs1(int u, int p){
for(auto [v, w] : G[u]){
if(v == p) continue;
dep[v] = dep[u]+1;
qs[v] = qs[u]+w;
dfs1(v, u);
}
}
void dfs2(int u, int p, const int &K){
for(auto [v, w] : G[u]){
if(v == p) continue;
dfs2(v, u, K);
if(mp[v].size() > mp[u].size()){
swap(mp[v], mp[u]);
}
}
for(auto [v, w] : G[u]){
for(auto &[key, val] : mp[v]){
long long tmp = K-key+2ll*qs[u];
if(mp[u].find(tmp) != mp[u].end()){
ans = min(ans, val+mp[u][tmp]-2*dep[u]);
}
}
for(auto &[key, val] : mp[v]){
if(mp[u].find(key) != mp[u].end()){
mp[u][key] = min(mp[u][key], val);
} else {
mp[u][key] = val;
}
}
}
if(mp[u].find(K+qs[u]) != mp[u].end()){
ans = min(ans, mp[u][K+qs[u]]-dep[u]);
}
mp[u][qs[u]] = dep[u];
}
int best_path(int N, int K, int H[][2], int L[])
{
for(int i = 0; i < N-1; i++){
int u = H[i][0], v = H[i][1];
G[u].emplace_back(v, L[i]);
G[v].emplace_back(u, L[i]);
assert(L[i] != 0);
}
dep[0] = 1;
dfs1(0, -1);
// for(int i = 0; i < N; i++) cout << dep[i] << " " << qs[i] << "\n";
dfs2(0, -1, K);
if(ans >= INF) ans = -1;
return ans;
}
/*
int main(void){
int N, K; cin >> N >> K;
int H[N-1][2], L[N-1];
for(int i = 0; i < N-1; i++) cin >> H[i][0] >> H[i][1] >> L[i];
int res; cin >> res;
int cal = best_path(N, K, H, L);
cout << cal << " " << res << "\n";
}*/
