/**
* In the name of Allah
* We are nothing and you're everything
* Ya Muhammad!
**/
#include <bits/stdc++.h>
#include "race.h"
//#include "grader.cpp"
using namespace std;
using ll = long long;
#define all(x) begin(x), end(x)
//#define int ll
const int NN = 2e5+5;
vector<pair<ll, ll>> g[NN];
ll sz[NN], dep[NN];
ll sum[NN];
vector<ll> *vec[NN];
map<ll, ll> *mp[NN];
ll 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, bool ok = true) {
int mx = 0, big = -1;
for (auto i: g[a]) {
if (i.first != p && sz[i.first] > mx)mx = sz[i.first], big = i.first;
}
for (auto i: g[a]) {
if (i.first != p && i.first != big)dfs(i.first, a, 0);
}
if (~big) {
dfs(big, a, 1), mp[a] = mp[big], vec[a] = vec[big];
}
else mp[a] = new map<ll, ll>, vec[a] = new vector<ll>;
vec[a]->push_back(a);
(*mp[a])[sum[a]] = ((*mp[a])[sum[a]]==0?dep[a]: min(dep[a], (*mp[a])[sum[a]]));
map<ll, ll> temp = (*mp[a]);
if (temp[kk+sum[a]] != 0)res = min(res, temp[kk+sum[a]]-dep[a]);
for (auto i: g[a]) {
if (i.first == p || i.first == big)continue;
for (auto j: *vec[i.first]) {
vec[a]->push_back(j);
int h = sum[j]-sum[a];
if ((*mp[a])[sum[j]] == 0)(*mp[a])[sum[j]] = dep[j];
else ((*mp[a])[sum[j]]) = min((*mp[a])[sum[j]], dep[j]);
if (kk-h < 0)continue;
if (temp[sum[a]+kk-h+sum[a]] == 0)continue;
else res = min(res, temp[sum[a]+kk-h+sum[a]]+dep[j]-2*dep[a]);
}
temp = (*mp[a]);
}
if (!ok) {
for (auto i: *vec[a])(*mp[a])[sum[i]] = 0;
}
}
int best_path(int n, int k, int h[][2], int l[]) {
for (int i = 0; i < n; ++i) {
g[i].clear();
(*mp[i]).clear();
(*vec[i]).clear();
}
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]});
}
res = NN;
calc();
dfs();
return (res==NN?-1:res);
}
//int main() {
//int n; cin >> n >> kk;
//for (int i = 0; i < n-1; ++i) {
//int a, b, w; cin >> a >> b >> w;
//g[a].push_back({b, w});
//g[b].push_back({a, w});
//}
//dep[0] = 1;
//calc();
//dfs();
//cout << res;
//}
