#include "race.h"
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define all(x) ((x).begin(), (x).end())
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int MAXN = 2e5 + 5;
const int INF = 1e9;
const ll MOD = 1e9 + 7;
int N, sz[MAXN], ans, K;
vector<pii> G[MAXN];
bool del[MAXN];
map<int, int> mp;
int szdfs(int cur, int par) {
sz[cur] = 1;
for(auto i : G[cur]) if(!del[i.fi] && i.fi != par) sz[cur] += szdfs(i.fi, cur);
return sz[cur];
}
int cdfs(int cur, int par, int cap) {
for(auto i : G[cur]) if(!del[i.fi] && i.fi != par && sz[i.fi] > cap) return cdfs(i.fi, cur, cap);
return cur;
}
void dfs(int cur, int par, int dis, int cnt) {
if(dis > K) return;
if(mp.find(K - dis) != mp.end()) ans = min(ans, mp[K - dis] + cnt);
for(auto i : G[cur]) if(!del[i.fi] && i.fi != par) dfs(i.fi, cur, dis + i.se, cnt+1);
}
void add(int cur, int par, int dis, int cnt) {
if(dis > K) return;
if(mp.find(dis) == mp.end()) mp[dis] = cnt;
else mp[dis] = min(mp[dis], cnt);
for(auto i : G[cur]) if(!del[i.fi] && i.fi != par) add(i.fi, cur, dis + i.se, cnt+1);
}
void solve(int cur) {
mp.clear();
mp[0] = 0;
for(auto i : G[cur]) if(!del[i.fi]) dfs(i.fi, cur, i.se, 1), add(i.fi, cur, i.se, 1);
}
void decompose(int root, int par) {
int cap = szdfs(root, 0);
int cen = cdfs(root, 0, cap / 2);
del[cen] = 1;
solve(cen);
for(auto i : G[cen]) if(!del[i.fi]) decompose(i.fi, cen);
}
int best_path(int _N, int _K, int H[][2], int L[]) {
N = _N; K = _K;
for(int i=0; i<N-1; i++) {
int a = H[i][0]+1, b = H[i][1]+1, c = L[i];
G[a].push_back(pii(b, c)); G[b].push_back(pii(a, c));
}
ans = 1e9;
decompose(1, 0);
if(ans == 1e9) return -1;
return ans;
}
