#include <bits/stdc++.h>
using namespace std;
// #define int long long
#define ll long long
const int MX = 2e5+1;
map<ll,int> col[MX];
vector<pair<int,ll>> adj[MX];
ll ans = 1e9, k, n;
ll w[MX], dep[MX];
void init(int cur,int par,ll dis,ll dp){
w[cur] = dis;
dep[cur] = dp++;
for(pair<int,ll>& nxt:adj[cur]){
if(nxt.first != par){
init(nxt.first,cur,dis+nxt.second,dp);
}
}
}
void dfs(int cur,int par){
if(w[cur] == k){
ans = min(ans,dep[cur]);
}
col[cur][w[cur]] = dep[cur];
for(pair<int,ll>& nxt:adj[cur]){
int nx = nxt.first;
if(nx == par) continue;
dfs(nx,cur);
if(col[cur].size() < col[nx].size()){
swap(col[cur],col[nx]);
}
ll req = k + 2*w[cur];
for(auto cols:col[nx]){
ll rem = req - cols.first;
if(col[cur].count(rem)){
ans = min(ans,cols.second+col[cur][rem] - 2ll*dep[cur]);
}
if(!col[cur].count(cols.first) || col[cur][cols.first] > cols.second){
col[cur][cols.first] = cols.second;
}
}
}
}
int best_path(int N, int K, int edges[][2], int weights[]) {
n = N;
k = K;
ans = 1e9;
for (int i = 0; i < n - 1; i++) {
int u = edges[i][0];
int v = edges[i][1];
u++,v++;
adj[u].push_back({v, weights[i]});
adj[v].push_back({u, weights[i]});
}
init(1,0,0,0);
dfs(1,0);
return ans > N ? -1 : ans;
}
