#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define ii pair<int,int>
const int ms = 2e5 + 10;
ll dis[ms], ans, k, n, sz[ms], h[ms];
vector<ii> g[ms];
map<ll, ll> mp;
void insere(int u){
if(mp.find(dis[u]) != mp.end()) mp[dis[u]] = min(mp[dis[u]], h[u]);
else mp[dis[u]] = h[u];
}
void put(int u, int p){
insere(u);
for(auto [v, w] : g[u]){
if(v == p) continue;
put(v, u);
}
}
void qry(int u, int p, int q){
if(mp.find(2ll*dis[q] - dis[u] + k) != mp.end()){
ll now = mp[2ll*dis[q] - dis[u] + k] + h[u] - 2*h[q];
if(ans == -1 || ans > now) ans = now;
}
for(auto [v, w] : g[u]){
if(v == p) continue;
qry(v, u, q);
}
}
void dfs(int u=0, int p=-1, bool keep = false){
int big = -1;
for(auto [v, w] : g[u]){
if(v == p) continue;
if(big == -1 || sz[big] < sz[v]) big = v;
}
for(auto [v, w] : g[u]){
if(v == p || v == big) continue;
dfs(v, u, false);
}
if(big != -1) dfs(big, u, true);
if(mp.find(2ll*dis[u] - dis[u] + k) != mp.end()){
ll now = mp[2ll*dis[u] - dis[u] + k] + h[u] - 2*h[u];
if(ans == -1 || ans > now) ans = now;
}
insere(u);
for(auto [v, w] : g[u]){
if(v == p || v == big) continue;
qry(v, u, u);
put(v, u);
}
if(!keep) mp.clear();
}
int getSz(int u=0, int p=-1, ll d=0, int height =0){
sz[u] = 1;
h[u] = height;
dis[u] = d;
for(auto [v, w] : g[u]){
if(v == p) continue;
sz[u] += getSz(v, u, d+w, height +1);
}
return sz[u];
}
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;
getSz();
dfs();
return ans;
}
// signed main(){
// cin.tie(0);
// ios::sync_with_stdio(0);
// cin >> n >> k;
// for(int i=1; i<n; i++){
// int a, b, w;
// cin >>a >> b >> w;
// g[a].push_back(ii(b, w));
// g[b].push_back(ii(a, w));
// }
// ans = -1;
// getSz();
// dfs();
// cout << ans << endl;
// }
