#include <bits/stdc++.h>
#include "race.h"
using namespace std;
using vi = vector <int>;
using pii = pair <int, int>;
#define pb push_back
#define F first
#define S second
#define N 200005
int n, k, ans = N, sz[N], mx[N], centroid;
map <int, int> dist;
bool used[N];
vector <pii> edg[N];
void get_size(int u, int p){
sz[u] = 1;
mx[u] = 0;
for (pii v : edg[u])
if (v.F != p && !used[v.F]){
get_size(v.F, u);
mx[u] = max(mx[u], sz[v.F]);
sz[u] += sz[v.F];
}
mx[u] = max(mx[u], n - sz[u]);
}
void get_centroid(int u, int p){
for (pii v : edg[u])
if (v.F != p && !used[v.F])
get_centroid(v.F, u);
if (mx[u] <= (n + 1) / 2) centroid = u;
}
void calc(int u, int p, int lenght, int distance){
if(distance > k) return;
for (pii v : edg[u])
if (v.F != p && !used[v.F])
calc(v.F, u, lenght + 1, distance + v.S);
if (dist.count(k - distance))
ans = min (ans, lenght + dist[k - distance]);
}
void add(int u, int p, int lenght, int distance){
if(distance > k) return;
for (pii v : edg[u])
if (v.F != p && !used[v.F])
add(v.F, u, lenght + 1, distance + v.S);
if (!dist.count(distance)) dist[distance] = lenght;
else dist[distance] = min(dist[distance], lenght);
}
void solve(int u){
dist.clear();
dist[0] = 0;
get_size(u, -1);
get_centroid(u, -1);
used[centroid] = 1;
get_size(centroid, -1);
for (pii v : edg[centroid])
if (!used[v.F]){
calc(v.F, centroid, 1, v.S);
add(v.F, centroid, 1, v.S);
}
for (pii v : edg[centroid])
if (!used[v.F]){
n = sz[v.F];
solve(v.F);
}
}
int best_path(int s, int K, int H[][2], int L[]){
n = s;
k = K;
for (int i = 0;i < n - 1;i++){
edg[H[i][0]].pb({H[i][1], L[i]});
edg[H[i][1]].pb({H[i][0], L[i]});
}
solve(0);
return ans == N ? -1 : ans;
}
