#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = (int)2e5 + 5;
const int M = (int)1e6 + 5;
const int inf = (int)1e9;
int h[N + 1][2], l[N + 1];
set<pair<int, int> > G[N];
int n, k, sz[N], exist[M], edgecnt[M], tt;
int dfs(int u, int p) {
sz[u] = 1;
for(auto it : G[u]) if(it.first != p) {
sz[u] += dfs(it.first, u);
}
return sz[u];
}
int centroid(int u, int p, int nn) {
for(auto it : G[u]) if(it.first != p) {
if(sz[it.first] > nn / 2) return centroid(it.first, u, nn);
}
return u;
}
int dfs2(int u, int p, int d, int cnt, int t, vector<pair<int, int> >& v) {
int want = k - d, ans = inf;
if(want >= 0 && exist[want] == t) {
ans = min(ans, cnt + edgecnt[want]);
}
if(d <= k) {
v.push_back({d, cnt});
for(auto it : G[u]) if(it.first != p) {
ans = min(ans, dfs2(it.first, u, d + it.second, cnt + 1, t, v));
}
}
return ans;
}
int Solve(int u, int p) {
int nn = dfs(u, p);
int c = centroid(u, p, nn);
int ans = inf;
int t = ++tt;
exist[0] = t; edgecnt[0] = 0;
for(auto it : G[c]) { // dfs one subtree at a time
vector<pair<int, int> > tmp;
ans = min(ans, dfs2(it.first, c, it.second, 1, t, tmp));
for(auto itt : tmp) {
if(exist[itt.first] != t || (exist[itt.first] == t && edgecnt[itt.first] > itt.second)) {
exist[itt.first] = t;
edgecnt[itt.first] = itt.second;
}
}
}
vector<pair<int, int> > tmp(G[c].begin(), G[c].end());
for(auto it : tmp) {
G[c].erase(it); G[it.first].erase({c, it.second});
ans = min(ans, Solve(it.first, c));
}
return ans;
}
int best_path (int n, int k, int h[][2], int l[])
{
for (int i = 0; i < n - 1; ++i)
{
G[h[i][0]].insert({h[i][1], l[i]});
G[h[i][1]].insert ({h[i][0], l[i]});
}
tt = 0;
int ans = Solve(0, -1);
if (ans == inf)ans = -1;
return ans;
cout << (ans == inf ? -1 : ans) << '\n';
}
