#include <bits/stdc++.h>
#include "race.h"
typedef long long ll;
using namespace std;
#define vint vector<int>
#define all(v) v.begin(), v.end()
#define MOD 1000000007
#define MOD2 998244353
#define MX 1000000000
#define MXL 1000000000000000000
#define PI (ld)2*acos(0.0)
#define nax 200005
#define pb push_back
#define sc second
#define fr first
//#define int long long
//#define endl '\n'
#define ld long double
#define NO cout << "NO" << endl
#define YES cout << "YES" << endl
vector<pair<int, ll>> adj[200005];
int n_glob;
int k_glob;
int size_sub[200005];
int del[200005];
void calc(int u, int par)
{
size_sub[u] = 1;
for(auto v : adj[u])
{
if(del[v.fr] == 0 && v.fr != par)
{
calc(v.fr, u);
size_sub[u]+=size_sub[v.fr];
}
}
}
int find_centroid(int u, int size, int par)
{
for(auto v : adj[u])
{
if(v.fr != par && del[v.fr] == 0 && size_sub[v.fr] > size)
{
return find_centroid(v.fr, size, u);
}
}
return u;
}
int ans = INT_MAX;
map<ll, int> cnt;
void dfs(int u, int par, ll weight, int type, int depth){
if(weight > k_glob)return;
if(type == 0){
if(cnt.count(k_glob - (int)weight)){
ans = min(ans, cnt[k_glob - weight] + depth);
}
}
else{
if(!cnt.count((int)weight))cnt[(int)weight] = depth;
else cnt[weight] = min(cnt[weight], depth);
}
for(auto x: adj[u]){
ll v = x.first, w = x.second;
if(v == par || del[v])continue;
dfs((int)v, u, weight + w, type, depth + 1);
}
}
void assign(int u)
{
calc(u, -1);
int centroid = find_centroid(u, size_sub[u] / 2, -1);
del[centroid] = 1;
cnt.clear();
cnt[0] = 0;
for(auto x : adj[centroid])
{
if(del[x.fr] == 1)
{
continue;
}
dfs(x.fr, -1, x.sc, 0, 1);
dfs(x.fr, -1, x.sc, 1, 1);
}
for(auto x : adj[centroid])
{
if(del[x.fr] == 0)
{
assign(x.fr);
}
}
}
int best_path(int n, int k, int h[][2],int l[])
{
ans = INT_MAX;
n_glob = n;
k_glob = k;
for(int i = 0; i <= n; i++)
{
adj[i].clear();
del[i] = 0;
size_sub[i] = 0;
}
cnt.clear();
for(int i = 0; i < n-1; i++)
{
adj[h[i][0]].pb({h[i][1], l[i]});
adj[h[i][1]].pb({h[i][0], l[i]});
}
assign(0);
if(ans == INT_MAX)
{
return -1;
}
return ans;
}
/*
int32_t main(){
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];
}
for(int i = 0; i < n-1; i++)
{
cin >> l[i];
}
cout << best_path(n, k, h, l) << endl;
}
*/
/*
3 3
0 1
0 2
1 1
4 3
0 1
1 2
1 3
1 2 4
11 12
0 1
0 2
2 3
3 4
4 5
0 6
6 7
6 8
8 9
8 10
3 4 5 4 6 3 2 5 6 7
*/
