#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef unsigned int uint;
typedef vector<int> vi;
typedef vector< vector <int> > vvi;
typedef pair<int, int> pii;
typedef pair < pair < int, int >, int > piii;
typedef pair < pair <int, int > , pair <int, int> > piiii;
typedef pair<ll, ll> pll;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
#define FOR(i,a,b) for(int i = a; i < b; i ++)
#define RFOR(i,a,b) for(int i = a-1; i >= b; i --)
#define all(a) a.begin(), a.end()
#define endl '\n';
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define ff first
#define ss second
vector<vector<pair<int, ll>>> adj;
vector<ll> dep, dist;
vector<map<ll, ll>> paths;
ll N, K;
ll ans = 1e9;
void dfs(int u, int p, ll d, ll ds) {
dep[u] = d;
dist[u] = ds;
for(auto x : adj[u]) {
ll w = x.ss;
int v = x.ff;
if(v != p) {
dfs(v, u, d + 1, ds + w);
}
}
}
void dfs2(int u, int p, ll d, ll ds) {
ll tar = K + 2 * ds;
paths[u][ds] = d;
for(auto x : adj[u]) {
ll w = x.ss;
int v = x.ff;
if(v != p) {
dfs2(v, u, d + 1, ds + w);
if(paths[v].size() > paths[u].size()) {
swap(paths[u], paths[v]);
}
for(auto y : paths[v]) {
if(paths[u].count(tar - y.ff)) {
ans = min(ans, paths[u][tar-y.ff] + y.ss - 2 * d);
}
}
for(auto y : paths[v]) {
if(paths[u].count(y.ff)) {
paths[u][y.ff] = min(paths[u][y.ff], y.ss);
} else {
paths[u][y.ff] = y.ss;
}
}
}
}
if(paths[u].count(K + ds)) {
ans = min(ans, paths[u][K+ds] - d);
}
}
int best_path(int n, int k, int edges[][2], int weights[]) {
adj.resize(n);
dist.resize(n);
dep.resize(n);
paths.resize(n);
K = k;
FOR(i,0,n-1) {
ll u = edges[i][0];
ll v = edges[i][1];
ll w = weights[i];
adj[u].pb({v,w});
adj[v].pb({u,w});
}
dfs(0,0,0,0);
dfs2(0,0,0,0);
if(ans == 1e9) ans = -1;
return ans;
}
