#include <bits/stdc++.h>
using namespace std;
map<int,long long> mp[300005] ;
vector<pair<int,long long>> adj[300005];
long long target = 0,sum[300005],height[300005],ans = 1e9,n,k;
void precomp(int nod, int p, int hd)
{
height[nod] = hd ;
for ( auto u : adj[nod] )
{
if ( u.first != p )
{
sum[u.first] += sum[nod] + u.second;
precomp(u.first,nod,hd + 1);
}
}
}
void small(int nod,int p )
{
mp[nod][sum[nod]] = height[nod];
long long real_target = target + 2 * sum[nod];
for ( auto u : adj[nod] )
{
if ( u.first != p )
{
small(u.first,nod);
}
}
for ( auto u : adj[nod] )
{
if( u.first != p )
{
if( mp[u.first].size() > mp[nod].size())
swap(mp[nod],mp[u.first]);
for ( auto k : mp[u.first] )
{
long long real = real_target - k.first ;
if ( mp[nod].find(real) != mp[nod].end())
{
//cout << nod << " " << u.first << " " << k.first << " " << k.second << '\n';
ans = min ( ans, k.second + mp[nod][real] - 2 * height[nod]);
}
}
for ( auto k : mp[u.first])
{
if( mp[nod].find(k.first) == mp[nod].end() )
mp[nod][k.first] = k .second;
else
mp[nod][k.first] = min(mp[nod][k.first],k.second);
}
}
}
/*if( nod == 6)
{
cout << mp[nod][real_target]<< '\n';
}*/
}
int best_path(int N, int K, int H[][2], int L [] )
{
if( K == 1 )
{
return 0 ;
}
target =K ;
for ( int i = 0; i < N - 1 ; i ++ )
{
adj[H[i][1]].push_back({H[i][0],L[i]});
adj[H[i][0]].push_back({H[i][1],L[i]});
}
precomp(0,-1,1);
small(0,-1);
if ( ans == 1e9 )
return -1;
else
return ans;
}
//int v[200005];
/*int main()
{
cin >> n >> k;
for ( int i = 1; i < n ; i ++ )
{
cin >> h[i][0] >> h[i][1] >> v[i] ;
}
cout << best_path(n,k,h,v);
return 0;
}*/
