/**
* In the name of Allah
* We are nothing and you're everything
* Ya Muhammad!
**/
#include <bits/stdc++.h>
#include "race.h"
//#include "grader.cpp"sdafasdfasdfsd
using namespace std;
using ll = long long;
#define all(x) begin(x), end(x)
//#define int ll
const int NN = 2e5+1;
vector<pair<ll, int>> g[NN];
int sz[NN], dep[NN];
ll sum[NN];
vector<map<ll, int>*> mp;
int res = NN;
void calc(int a = 0, int p = 0) {
sz[a] = 1;
for (auto i: g[a]) {
if (i.first == p)continue;
dep[i.first] = dep[a]+1;
sum[i.first] = sum[a]+i.second;
calc(i.first, a);
sz[a] += sz[i.first];
}
}
int kk;
void dfs(int a = 0, int p = 0) {
int big = -1;
for (auto i: g[a])
if (i.first != p && (!~big || sz[i.first] > sz[big]))big = i.first;
if (~big)dfs(big, a), mp[a] = mp[big];
else mp[a] = new map<ll, int> ();
(*mp[a])[sum[a]] = dep[a];
if (mp[a]->find(kk+sum[a]) != mp[a]->end())res = min(res, (*mp[a])[kk+sum[a]]-dep[a]);
for (auto [i, w]: g[a]) {
if (i == p || i == big)continue;
dfs(i, a);
for (auto [j, d]: *mp[i]) {
ll aa = kk-(j-sum[a])+sum[a];
if (mp[a]->find(aa) != mp[a]->end())res = min(res, (*mp[a])[aa]+d-2*dep[a]);
}
for (auto [j, d]: *mp[i]) {
if (mp[a]->find(j) == mp[a]->end())(*mp[a])[j] = d;
else (*mp[a])[j] = min((*mp[a])[j], d);
}
}
}
int best_path(int n, int k, int h[][2], int l[]) {
dep[0] = 1;
kk = k;
for (int i = 0; i < n-1; ++i) {
g[h[i][0]].push_back({h[i][1], l[i]});
g[h[i][1]].push_back({h[i][0], l[i]});
}
mp.assign(n, {});
res = NN;
calc();
dfs();
for (int i = 0; i < n; ++i) {
g[i].clear();
}
return (res==NN?-1:res);
}
