#include "race.h"
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
typedef long long ll;
const ll INF = 1e18;
const ll MOD = 1e9 + 7;
const ll MAXN = 2e2 + 5;
const ll LOG = 30;
#define vll vector <ll>
#define pll pair <ll, ll>
#define fi first
#define se second
#define endl '\n'
#define debug(x) cout << #x << " " << (x) << endl;
ll n, k;
vector <vector <pll> > adj (MAXN);
ll ans = INF;
ll dp [MAXN], dep [MAXN];
vector <set <pll>> st (MAXN);
void tun(ll x, ll v, ll dmn){
// k = v + ... - 2*dp[x]
// k + 2*dp[x] - v = ...
ll cnt = k + 2*dp[x] - v;
auto it = st[x].lower_bound({cnt, 0});
if((*it).fi == cnt){
ans = min(ans, dmn+(*it).se-2*dep[x]);
}
}
void add(ll x, ll v, ll dmn){
auto it = st[x].lower_bound({v, 0});
if((*it).fi == v){
dmn = min(dmn, (*it).se);
st[x].erase(it);
}
st[x].insert({v, dmn});
}
void dfs(ll x, ll px){
for(auto [y, w] : adj[x]){
if(y == px) continue;
dp[y] = dp[x] + w;
dep[y] = dep[x] + 1;
dfs(y, x);
if((ll)st[x].size() < (ll)st[y].size()) swap(st[x], st[y]);
for(auto [v, dmn] : st[y]) tun(x, v, dmn);
for(auto [v, dmn] : st[y]) add(x, v, dmn);
}
tun(x, dp[x], dep[x]);
add(x, dp[x], dep[x]);
}
int best_path(int N, int K, int H[][2], int L[])
{
n = N;
k = K;
for(ll i = 0; i < n-1; i++){
auto [u, v] = H[i];
ll w = L[i];
adj[u].push_back({v, w});
adj[v].push_back({u, w});
}
dfs(0, -1);
return (ans == INF) ? -1 : ans;
}
