#define mocua(inp, out) if(fopen(inp,"r")){freopen(inp,"r",stdin);freopen(out,"w",stdout);}
#include <iostream>
#include <cstdint>
#include <climits>
#include <vector>
#include <map>
using namespace std;
int numNode, desiredLength;
vector<int> e[int(2e5+3)];
vector<pair<int,int>> elen[int(2e5+3)];
int ans = 1e9+69;
int sz[int(2e5+3)], bigchild[int(2e5+3)];
int length[int(2e5+3)], depth[int(2e5+3)];
void size(int u=0, int p=-1){
for(auto &[v,w] : elen[u])if(v!=p){
length[v] = length[u] + w;
depth[v] = depth[u] + 1;
size(v, u);
if(sz[v] > sz[bigchild[u]]) bigchild[u] = v;
}
}
map<int,int> mp[int(2e5+3)];
void process(int u=0, int p=-1){
// cout << u << ". " << length[u] << ' ' << depth[u] << '\n';
mp[u][length[u]] = depth[u];
for(int &v : e[u])if(v!=p){
process(v, u);
if(mp[u].size() < mp[v].size()) swap(mp[u], mp[v]);
for(auto &x : mp[v])
if(mp[u].find(2*length[u] + desiredLength - x.first) != mp[u].end()){
ans = min(ans, mp[u][2*length[u] + desiredLength - x.first] + x.second - 2*depth[u]);
// cout << length[u] << ' ' << x.first << ' ' << 2*length[u] + desiredLength - x.first << " ~ ";
// cout << x.second << ' ' << mp[u][2*length[u] + desiredLength - x.first] << endl;
}
for(auto &x : mp[v]){
if(mp[u].find(x.first) != mp[u].end())
mp[u][x.first] = min(mp[u][x.first], mp[v][x.first]);
else mp[u][x.first] = mp[v][x.first];
}
}
// cout << u << ". " << endl;
// for(auto &x : mp[u]) cout << x.first << ' ' << x.second << endl;
}
int best_path(int _numNode, int _desiredLength, int edge[][2], int edgeLength[]){
numNode = _numNode;
desiredLength = _desiredLength;
for(int i=0; i<numNode; ++i)
e[i].clear(),
elen[i].clear();
for(int i=0; i<numNode-1; ++i){
e[edge[i][0]].emplace_back(edge[i][1]);
e[edge[i][1]].emplace_back(edge[i][0]);
elen[edge[i][0]].emplace_back(edge[i][1], edgeLength[i]);
elen[edge[i][1]].emplace_back(edge[i][0], edgeLength[i]);
}
for(int i=0; i<numNode; ++i) bigchild[i] = numNode;
size();
process();
return (ans>=1e9 ? -1 : ans);
}
// int edge[int(2e5+3)][2];
// int edgeLength[int(2e5+3)];
// signed main()
// {
// cin.tie(0) -> sync_with_stdio(0);
// int n, k;
// cin >> n >> k;
// for(int i=0, u, v; i<n-1; ++i) cin >> edge[i][0] >> edge[i][1];
// for(int i=0; i<n-1; ++i) cin >> edgeLength[i];
// cout << best_path(n, k, edge, edgeLength);
// return 0;
// }
