#include <bits/stdc++.h>
#include "race.h"
using namespace std;
const int MX = 1e6;
vector<vector<pair<int,int>>> g;
vector<int> sz, dead;
int dfs_sz(int v, int p){
sz[v] = 1;
for(auto [u, w]: g[v]) if(u != p && !dead[u]){
sz[v] += dfs_sz(u, v);
}
return sz[v];
}
int cent(int v, int p, int n){
for(auto [u, w]: g[v]) if(u != p && !dead[u] && sz[u] > n / 2){
return cent(u, v, n);
}
return v;
}
void dfs(int v, int p, int ws, vector<pair<int,int>> &ps, int ln){
if(ws > MX) return;
ps.emplace_back(ws, ln);
for(auto [u, w]: g[v]) if(u != p && !dead[u]){
dfs(u, v, ws + w, ps, ln + 1);
}
}
int dc(int v, int k){
int n = dfs_sz(v, -1);
int c = cent(v, -1, n);
dead[c] = 1;
vector<vector<pair<int,int>>> ps;
for(auto [u, w]: g[c]) if(!dead[u]){
ps.emplace_back();
dfs(u, c, w, ps.back(), 1);
}
int ans = 1e9;
map<int,int> mins;
mins[0] = 0;
for(auto chld: ps){
for(auto [x, ln]: chld){
if(k - x >= 0){
if(mins.find(k - x) != mins.end()) ans = min(ans, mins[k - x] + ln);
}
}
for(auto [x, ln]: chld){
if(mins.find(x) != mins.end()) mins[x] = min(mins[x], ln);
else mins[x] = ln;
}
}
for(auto [u, w]: g[c]) if(!dead[u]){
ans = min(ans, dc(u, k));
}
return ans;
}
int best_path(int n, int k, int h[][2], int l[]){
g.resize(n);
sz.resize(n);
dead.resize(n);
for(int i = 0; i < n - 1; i++){
g[h[i][0]].emplace_back(h[i][1], l[i]);
g[h[i][1]].emplace_back(h[i][0], l[i]);
}
int ans = dc(0, k);
if(ans >= 1e9) ans = -1;
return ans;
}
