#include <bits/stdc++.h>
typedef long long ll;
using namespace std;
constexpr ll maxN = 2e5+10;
constexpr ll inf = 1e15;
vector<pair<ll, ll>> adj[maxN];
ll res = inf, k;
map<ll, ll> dfs(ll v, ll p, ll konst, ll dep) {
map<ll, ll> mp;
mp[konst]=dep;
for(auto i : adj[v]) {
if(i.first==p)continue;
map<ll, ll> tmp = dfs(i.first, v, i.second+konst, dep+1);
if(tmp.size()>mp.size())swap(mp, tmp);
for(auto x : tmp) {
ll val = x.first;
ll dep1 = x.second;
ll needed = k+2*konst-val;
if(mp.count(needed)) {
ll dep2 = mp[needed];
res=min(res, dep1+dep2-2*dep);
}
}
for(auto x : tmp) {
if(!mp.count(x.first))mp[x.first]=x.second;
else mp[x.first]=min(x.second, mp[x.first]);
}
}
return mp;
}
int best_path(int N, int K, int H[][2], int L[])
{
k=K;
for(int i = 0; i < N-1; i++) {
ll aa = H[i][0], bb = H[i][1];
adj[aa].push_back({bb, L[i]});
adj[bb].push_back({aa, L[i]});
}
dfs(0, -1, 0, 0);
if(res==inf) {
return -1;
}
return res;
}
/*int nn, kk;
int H[maxN][2];
int L[maxN];
int solution;
int main()
{
cin>>nn>>kk;
for(int i = 0; i < nn-1; i++) {
cin>>H[i][0]>>H[i][1];
}
for(int i = 0; i < nn-1; i++) {
cin>>L[i];
}
cout<<best_path(nn,kk,H,L);
return 0;
}
*/
