#include "race.h"
/*
* Author : shora
*/
#include <bits/stdc++.h>
#define print(_v) for (auto &_ : _v) {cerr << _ << ' ';} cerr << endl;
using namespace std;
using ll = long long;
const int oo = 1e9;
const int N = 5e5, MAXK = 1e6;
struct C {
int v, w;
C(int v, int w): v(v), w(w) {}
};
vector<C> G[N];
int vis[N], size[N], f[MAXK + 1], dep[N];
int k;
int res = oo;
void find_size(int u, int e = -1) {
size[u] = 1;
for (C& c : G[u]) if (c.v != e && !vis[c.v]) {
find_size(c.v, u);
size[u] += size[c.v];
}
}
int centroid(int s, int u, int e = -1) {
for (C& c : G[u]) if (c.v != e && !vis[c.v])
if (size[c.v] > s / 2)
return centroid(s, c.v, u);
return u;
}
void get(int u, int e, int dis) {
if (k < dis)
return;
dep[u] = dep[e] + 1;
if (f[k - dis] != oo)
res = min(res, f[k - dis] + dep[u]);
for (C& c : G[u]) if (c.v != e && !vis[c.v]) {
get(c.v, u, dis + c.w);
}
}
void update(int u, int e, int dis) {
if (k < dis)
return;
f[dis] = min(f[dis], dep[u]);
for (C& c : G[u]) if (c.v != e && !vis[c.v]) {
update(c.v, u, dis + c.w);
}
}
void clear(int u, int e = -1, int dis = 0) {
if (k < dis)
return;
dep[u] = 0;
for (C& c : G[u]) if (c.v != e && !vis[c.v]) {
clear(c.v, u, dis + c.w);
}
f[dis] = oo;
}
void solve(int u) {
find_size(u);
u = centroid(size[u], u);
vis[u] = 1;
f[0] = 0;
for (C& c : G[u]) if (!vis[c.v]) {
get(c.v, u, c.w);
update(c.v, u, c.w);
}
clear(u);
for (C& c : G[u]) if (!vis[c.v])
solve(c.v);
}
int best_path(int n, int K, int H[][2], int L[]) {
k = K;
for (int i = 0, u, v, w; i < n-1; ++i) {
u = H[i][0]; v = H[i][1]; w = L[i];
G[u].push_back(C(v, w));
G[v].push_back(C(u, w));
}
for (int i = 1; i <= k; ++i)
f[i] = oo;
solve(0);
return res == oo ? -1 : res;
}
