#define ll long long
#define maxN 2000005
using namespace std;
#include <iostream>
#include<vector>
#include <climits>
#include<set>
#include<map>
//first = node, second = weight
vector<pair<int ,ll>> adj[maxN];
map<ll, int> sets[maxN];
vector<int> ord;
int p[maxN], lzN[maxN];
ll lzW[maxN];
void dfs(int node, int parent){
p[node] = parent;
for(pair<int, int> j: adj[node]){
if(j.first != parent){
dfs(j.first, node);
ord.push_back(j.first);
}
}
}
int best_path(int n, int k, int edges[][2], int weights[]){
// cin >> n >> k;
for (int i = 0; i < n - 1; ++i) {
// int a = 0, b = 0, w= 0;
// cin >> a >> b >> w;
int a = edges[i][0], b = edges[i][1], w = weights[i];
adj[a].push_back(make_pair(b, w));
adj[b].push_back(make_pair(a, w));
}
dfs(0, -1);
p[0] = -1;
ord.push_back(0);
int ans = INT_MAX;
for (int i = 0; i < n; ++i) {
int node = ord[i];
if(adj[node].size() == 1 && node != 0){
lzW[node] = 0;
lzN[node] = 0;
continue;
}
int bn = -1, bz = -1;
ll bw = 0;
for(pair<int, int> j : adj[node]){
if(j.first == p[node]) continue;
if((int)sets[j.first].size() > bz){
bz = (int)sets[j.first].size();
bn = j.first;
bw = j.second;
}
}
swap(sets[bn], sets[node]);
lzW[node] = lzW[bn] + bw;
lzN[node] = lzN[bn] + 1;
sets[node][bw - lzW[node]] = 1 - lzN[node];
if(bw == k){
ans = min(ans, 1);
}
for(pair<int, int> j: adj[node]){
if(j.first == p[node] || j.first == bn) continue;
for (auto const& a : sets[j.first]){
ll f = (k - (a.first + lzW[j.first] + j.second)) - lzW[node];
if(sets[node].find(f) != sets[node].end()){
ans = min(ans, a.second + lzN[j.first] + 1 + sets[node][f] + lzN[node]);
}
}
for (auto const& a : sets[j.first]){
ll f = (a.first + lzW[j.first] + j.second) - lzW[node];
if(sets[node].find(f) != sets[node].end()){
sets[node][f] = min(sets[node][f], a.second + lzN[j.first] + 1 - lzN[node]);
}else{
sets[node][f] = a.second + lzN[j.first] + 1 - lzN[node];
}
}
ll f = k - j.second;
if(sets[node].find(f) != sets[node].end()){
ans = min(ans, sets[node][f] + lzN[node] + 1);
}
sets[node][j.second - lzW[node]] = 1 - lzN[node];
}
if(sets[node].find(k - lzW[node]) != sets[node].end()){
ans = min(ans, sets[node][k - lzW[node]] + lzN[node]);
}
}
return (ans == INT_MAX) ? -1: ans;
}
//int main(){
// cout << best_path(0, 0, {}, 0);
//// int cE[10][2] = {{0, 1}, {0, 2}, {2,3}, {3,4}, {4,5}, {0, 6}, {}};
//// cout << best_path(11, 12, )
//}
