#define taskname "Race"
#include <bits/stdc++.h>
#define ll long long
#define ii pair<int,int>
#define ff first
#define ss second
using namespace std;
const int maxn = 2e5 + 10;
vector<ii> adj[maxn];
int sz[maxn], ban[maxn], m, ans = 1e9;
map<int,int> mp;
void DFSz(int u, int p = 0)
{
sz[u] = 1;
for (auto [v, c]: adj[u]) if (v != p && !ban[v]) DFSz(v, u), sz[u] += sz[v];
}
int getcen(int u, int need, int p = -1)
{
if (sz[u] <= need) return p;
ii big = {0, 0};
for (auto [v, c]: adj[u]) if (v != p && !ban[v]) big = max(big, {sz[v], v});
return getcen(big.ss, need, u);
}
void DFS(int u, int p, int dep, int type, int dis = 1)
{
if (type == 0)
{
if (mp.count(m - dep)) ans = min(ans, dis + mp[m-dep]);
}
else mp[dep] = (mp.count(dep) ? min(mp[dep], dis) : dis);
for (auto [v, c]: adj[u]) if (v != p && !ban[v]) DFS(v, u, dep+c, type, dis+1);
}
void solve(int u = 1)
{
DFSz(u);
u = getcen(u, sz[u]/2);
ban[u] = 1;
mp.clear();
mp[0] = 0;
for (auto [v, c]: adj[u]) if (!ban[v]) DFS(v, u, c, 0), DFS(v, u, c, 1);
for (auto [v, c]: adj[u]) if (!ban[v]) solve(v);
}
int best_path(int N, int K, int H[][2], int L[])
{
m = K;
for (int i=1; i<=N; i++) adj[i].clear(), ban[i] = 0;
for (int i=0; i<N-1; i++)
{
int u = H[i][0], v = H[i][1], c = L[i];
u++, v++;
adj[u].emplace_back(v, c);
adj[v].emplace_back(u, c);
}
solve();
return (ans == 1e9 ? -1 : ans);
}
//signed main()
//{
// ios_base::sync_with_stdio(false);
// cin.tie(nullptr); cout.tie(nullptr);
// int h[3][2] = {{0, 1}, {1, 2}, {2, 3}};
// int l[3] = {1, 2, 4};
// cout<<best_path(4, 3, h, l);
//}
