#include <bits/stdc++.h>
#define int long long
using namespace std;
int n; int t;
signed ans = 1e7;
unordered_map<int,int> adj[(int)2e5];
int off1[(int)2e5];
int off2[(int)2e5];
unordered_map<int, int> pth[(int)2e5];
void dfs(int i, int p){
for (auto const &pair1: adj[i]){
int c = pair1.first; int w = pair1.second;
if (c==p) continue;
dfs(c,i);
off1[c]+=w;
off2[c]+=1;
if (pth[i].size() < pth[c].size()){
swap(pth[i], pth[c]);
swap(off1[c], off1[i]);
swap(off2[c], off2[i]);
}
for (auto const & pr: pth[c]){
int s = pr.first; int l = pr.second;
if (pth[i].count(t-s-off1[c]-off1[i])) ans = min(ans,(signed)(l+pth[i][t-s-off1[c]-off1[i]]+off2[i]+off2[c]));
}
for (auto const & pr: pth[c]){
int s = pr.first; int l = pr.second;
if (pth[i].count(s-off1[i]+off1[c]))pth[i][s-off1[i]+off1[c]] = min(pth[i][s-off1[i]+off1[c]], l+off2[c]-off2[i]);
else pth[i][s-off1[i]+off1[c]] = l+off2[c]-off2[i];
}
}
}
signed best_path(signed sz, signed k, signed h[][2], signed l[]){
n = sz; t=k;
for (int i=0; i<n-1; i++){
int a = h[i][0]; int b = h[i][1];
adj[a][b] = l[i]; adj[b][a] = l[i];
}
for (int i=0; i<n; i++) pth[i][0] = 0;
for (int i=0; i<n; i++) off1[i] = 0;
for (int i=0; i<n; i++) off2[i] = 0;
dfs(0,0);
if (ans==(int)1e7) return -1;
return ans;
}
// signed main(){
// signed n= 11, k=12;
// signed h[n-1][2];
// signed 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);
// }
