#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define ii pair<int,int>
const int ms = 2e5 + 10;
ll h[ms], dis[ms], ans, k, n;
vector<ii> g[ms];
map<ll, ll > mp[ms];
void dfs(int u=0, int p=-1, ll d=0, int height =0){
mp[u][d]= height;
h[u] = height;
dis[u] = d;
for(auto [v, w] : g[u]){
if(v == p) continue;
dfs(v, u, d+w, height+1);
}
}
void sack(int u=0, int p=-1){
// dis[u] + target = k
// x + y - (2 * dis[u]) = k
// x + y = 2*dis[u] + k
// y = 2*dis[u] + k - x
for(auto [v, w] : g[u]){
if(v == p) continue;
sack(v, u);
if(mp[v].size() > mp[u].size()) mp[u].swap(mp[v]);
for(auto [x, y] : mp[v]){
if(mp[u].find(2ll*dis[u] + k - x) != mp[u].end()){
ll now = y + mp[u][2*dis[u] + k - x] - 2*h[u];
if(ans == -1 || ans > now) ans = now;
}
}
for(auto [x, y] : mp[v]){
if(mp[u].find(x) != mp[u].end()){
mp[u][x] = min(mp[u][x], y);
}
else mp[u][x] = y;
}
}
}
int best_path(int N, int K, int H[][2], int L[]){
k = K;
n = N;
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]});
}
ans = -1;
dfs();
sack();
return ans;
}
