#include "race.h"
#include <bits/stdc++.h>
#define X first
#define Y second
#define MP make_pair
#define ll long long
using namespace std;
const int MAXN = 2e5 + 12;
int answer, n, k, sz[MAXN], mx[MAXN];
map< int, int > act;
vector< pair< int, int > > graph[MAXN];
bool block[MAXN];
void dfs_sz(int v, int pr){
sz[v] = 1, mx[v] = 0;
for(pair<int, int> to: graph[v]){
if(to.X != pr && !block[to.X]){
dfs_sz(to.X, v), sz[v] += sz[to.X];
if(sz[mx[v]] < sz[to.X])
mx[v] = to.X;
}
}
}
int get_cent(int v){
int u = v;
while(sz[v] < sz[mx[u]] * 2)
u = mx[u];
return u;
}
void dfs_ans(int v, int pr, ll cost, int dist){
if(cost > k)
return;
if(act.count(k - cost))
answer = min(answer, dist + act[k - cost]);
for(pair<int, int> to: graph[v]){
if(to.X != pr && !block[to.X]){
dfs_ans(to.X, v, cost + to.Y, dist + 1);
}
}
}
void dfs_add(int v, int pr, ll cost, int dist){
if(cost > k)
return;
if(!act.count(cost) || act[cost] > dist)
act[cost] = dist;
for(pair<int, int> to: graph[v]){
if(to.X != pr && !block[to.X]){
dfs_add(to.X, v, cost + to.Y, dist + 1);
}
}
}
void cent(int v){
dfs_sz(v, v), v = get_cent(v), block[v] = 1;
act[0] = 0;
for(pair<int, int> to: graph[v]){
if(!block[to.X])
dfs_ans(to.X, v, to.Y, 1), dfs_add(to.X, v, to.Y, 1);
}
act.clear();
for(pair<int, int> to: graph[v]){
if(!block[to.X])
cent(to.X);
}
}
int best_path(int N, int K, int H[][2], int L[]){
n = N, k = K, answer = MAXN;
for(int i = 0;i < n - 1;i++){
graph[H[i][1] + 1].push_back(MP(H[i][0] + 1, L[i]));
graph[H[i][0] + 1].push_back(MP(H[i][1] + 1, L[i]));
}
cent(1);
if(answer == MAXN)
answer = -1;
return answer;
}
