#include "race.h"
#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
int n, k;
vector<pair<int, int> > adj[200005];
int cnt[200005], trip[200005];
int get_cnt(int now, int par) {
cnt[now] = 1;
for (auto &there : adj[now]) {
if (there.first == par || trip[there.first])continue;
cnt[now] += get_cnt(there.first, now);
}
return cnt[now];
}
int get_centroid(int now, int par,int c) {
for (auto &there : adj[now]) {
if (there.first == par || trip[there.first])continue;
if(cnt[there.first]>c)
return get_centroid(there.first, now, c);
}
return now;
}
void dfs(int now, int par, int weight, int depth, vector<pair<int, int> > &vec) {
vec.emplace_back(weight, depth);
for (auto &there : adj[now]) {
if (there.first == par || trip[there.first])continue;
dfs(there.first, now, weight + there.second, depth + 1, vec);
}
}
int solve(int now) {
get_cnt(now, -1);
int centroid = get_centroid(now, -1, cnt[now] / 2);
trip[centroid] = true;
int ret = inf;
map<int, int> mp;
mp[0] = 0;
for (auto &there : adj[centroid]) {
if (trip[there.first])continue;
vector<pair<int, int> > vec;
dfs(there.first, centroid, there.second, 1, vec);
for (auto x : vec)
if (mp.count(k - x.first))
ret = min(ret, x.second + mp[k - x.first]);
for (auto x : vec) {
if (!mp.count(x.first))
mp[x.first] = x.second;
else
mp[x.first] = min(mp[x.first], x.second);
}
}
for (auto &there : adj[centroid]) {
if (trip[there.first])continue;
ret = min(ret, solve(there.first));
}
return ret;
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N; k = K;
for (int i = 0; i < n - 1; i++) {
adj[H[i][0]].emplace_back(H[i][1], L[i]);
adj[H[i][1]].emplace_back(H[i][0], L[i]);
}
int ret = solve(0);
return ret == inf ? -1 : ret;
}
