#include <bits/stdc++.h>
#include "race.h"
using namespace std;
#define lli long long int
#define MP make_pair
#define pb push_back
#define REP(i,n) for(int (i) = 0; (i) < (n); (i)++)
#pragma optimize('O1,O2,O3, Ofast');
const double EPS = 0.00001;
const int INF = 1e9+500;
const int ALPH = 26;
const int MOD = 1e9+7;
const int M = 1e6+5;
const int NMAX = 2e5+5;
int n,m,q, k;
array<int,2> cnt[M];
int ans = INF;
int vis[NMAX], subt[NMAX];
vector<vector<array<int,2> > > adj;
vector<int> centers;
int curc = 0;
inline void subtdfs(int node, int par) {
subt[node] = 1;
for(auto c : adj[node]) {
if(c[0] == par) continue;
if(vis[c[0]]) continue;
subtdfs(c[0], node);
subt[node] += subt[c[0]];
}
}
inline int cdfs(int node, int par, int sz) {
for(auto c : adj[node]) {
if(c[0] == par) continue;
if(vis[c[0]]) continue;
if(subt[c[0]]*2 >= sz) {
return cdfs(c[0], node, sz);
}
}
return node;
}
inline void find_centroids() {
subtdfs(1, 0);
int tmp = cdfs(1, 0, subt[1]);
centers.pb(tmp);
int ind = 0;
vis[tmp] = 1;
while(ind < centers.size()) {
for(auto c : adj[centers[ind]]) {
if(vis[c[0]]) continue;
subtdfs(c[0], 0);
tmp = cdfs(c[0], 0, subt[c[0]]);
vis[tmp] = 1;
centers.pb(tmp);
}
ind++;
}
}
inline void dfs(int node ,int par, int cost, int leng) {
if(leng > k) return;
if(cnt[leng][1] != curc) {
cnt[leng] = {cost, curc};
}
cnt[leng][0] = min(cnt[leng][0], cost);
for(auto c : adj[node]) {
if(c[0] == par) continue;
if(vis[c[0]]) continue;
dfs(c[0], node, cost + 1, leng + c[1]);
}
}
inline void dfs2(int node, int par, int cost, int leng) {
if(leng > k) return;
if(cnt[k - leng][1] == curc) {
ans = min(ans ,cnt[k - leng][0] + cost);
}
for(auto c : adj[node]) {
if(c[0] == par) continue;
if(vis[c[0]]) continue;
dfs2(c[0], node, cost + 1, leng + c[1]);
}
}
inline void find_paths() {
for(int j = 0; j<k+1; j++) {
cnt[j][0] = INF;
cnt[j][1] = 0;
}
for(int i = 0; i<=n; i++) vis[i] = 0;
for(auto i : centers) {
cnt[0][0] = 0; cnt[0][1] = i;
curc = i;
vis[i] = 1;
for(auto c : adj[i]) {
if(vis[c[0]]) continue;
dfs2(c[0], i, 1, c[1]);
dfs(c[0], i, 1, c[1]);
}
}
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N;
adj.resize(n+1);
k = K;
for(int i = 0; i<n-1; i++) {
H[i][0]++;
H[i][1]++;
adj[H[i][0]].pb({H[i][1], L[i]});
adj[H[i][1]].pb({H[i][0], L[i]});
}
find_centroids();
find_paths();
if(ans == INF) ans = -1;
return ans;
}
