#include "race.h"
#include <bits/stdc++.h>
using namespace std;
const int INF = 1E9;
int k, ans = INF;
vector<vector<pair<int, int>>> g;
vector<int> sz, dep, to, ds;
vector<bool> centroid;
void calc(int u, int p) {
sz[u] = 1;
for (auto [v, w] : g[u])
if (v ^ p && !centroid[v])
calc(v, u), sz[u] += sz[v];
}
int findcentroid(int u, int p, const int &s) {
for (auto [v, w] : g[u])
if (v ^ p && !centroid[v] && sz[v] > s)
return findcentroid(v, u, s);
return u;
}
void calcdep(int u, int p, int d) {
dep[u] = d;
for (auto [v, w] : g[u])
if (v ^ p && !centroid[v])
calcdep(v, u, d + 1);
}
void addmx(int u, int p, int length) {
if (length > k) return;
ds[length] = min(ds[length], dep[u]);
to.push_back(length);
for (auto [v, w] : g[u])
if (v ^ p && !centroid[v])
addmx(v, u, length + w);
}
void calcmx(int u, int p, int length) {
if (length > k) return;
ans = min(ans, dep[u] + ds[k - length]);
for (auto [v, w] : g[u])
if (v ^ p && !centroid[v])
calcmx(v, u, length + w);
}
void decompose(int u) {
calc(u, u);
int x = findcentroid(u, u, sz[u] >> 1);
calcdep(x, x, 0);
centroid[x] = 1;
for (auto [v, w] : g[x]) {
if (!centroid[v]) {
calcmx(v, x, w);
addmx(v, x, w);
}
}
ans = min(ans, ds[k]);
for (int i : to) ds[i] = INF;
to.clear();
for (auto [v, w] : g[x])
if (!centroid[v])
decompose(v);
}
int best_path(int n, int k_, int h[][2], int l[]) {
k = k_;
g = vector<vector<pair<int, int>>> (n), centroid = vector<bool> (n), dep = vector<int> (n), ds = vector<int>(k + 1, INF), sz = dep;
for (int i = 0; i < n - 1; i++) {
int u = h[i][0], v = h[i][1], w = l[i];
g[u].push_back({v, w});
g[v].push_back({u, w});
}
decompose(0);
return ans == INF ? -1 : ans;
}
