#include "race.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define FOR(i, a, b) for(int i = (int)a; i <= (int)b; i++)
#define DEC(i, a, b) for(int i = (int)a; i >= (int)b; i--)
typedef pair<int, int> pi;
typedef pair<int, pi> pii;
typedef pair<pi, pi> pipi;
#define f first
#define s second
typedef vector<int> vi;
typedef vector<pi> vpi;
typedef vector<pii> vpii;
#define pb push_back
#define pf push_front
#define all(v) v.begin(), v.end()
#define disc(v) sort(all(v)); v.resize(unique(all(v)) - v.begin());
#define INF (int) 1e9 + 100
#define LLINF (ll) 1e18
#define fastio ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
int n, k, sz[200005], coun, ans = INF;
int newdist[1000005], dist[1000005];
bool vis[200005];
vpi adj[200005];
int sztrsz(int x, int p) {
sz[x] = 1;
for (auto it:adj[x]) if (!vis[it.f] and it.f != p) sz[x] += sztrsz(it.f, x);
return sz[x];
}
int findcent(int x, int p, int n) {
for (auto it:adj[x]) {
if (vis[it.f]) continue;
if (it.f != p and sz[it.f] > n/2 and !vis[it.f]) return findcent(it.f, x, n);
}
return x;
}
void dfsend(int x, int p, int d, int num) {
if (d == k) ans = min(ans, num);
if (d > k) return;
for (auto it:adj[x]) if (!vis[it.f] and it.f != p) dfsend(it.f, x, d+it.s, num+1);
}
vi cur, temp;
void dfs(int x, int p, int d, int num) {
if (d == k) ans = min(ans, num);
if (d > k) return;
if (dist[k-d] != INF) ans = min(ans, num + dist[k-d]);
newdist[d] = min(newdist[d], num);
cur.pb(d); temp.pb(d);
for (auto it:adj[x]) if (it.f != p and !vis[it.f]) dfs(it.f, x, d + it.s, num+1);
}
void solve(int x) {
int cent = findcent(x, -1, sztrsz(x, -1));
dfsend(cent, -1, 0, 0);
for (auto it:adj[cent]) if (!vis[it.f]) {
dfs(it.f, cent, it.s, 1);
for (auto d:temp) dist[d] = min(dist[d], newdist[d]);
temp.clear();
}
for (auto it:cur) dist[it] = newdist[it] = INF;
cur.clear();
vis[cent] = 1;
for (auto it:adj[cent]) if (!vis[it.f]) solve(it.f);
}
int best_path(int N, int K, int H[][2], int L[]) {
n = N, k = K;
FOR(i, 0, n-2) {
adj[H[i][0]].pb(pi(H[i][1], L[i]));
adj[H[i][1]].pb(pi(H[i][0], L[i]));
}
FOR(i, 0, K) dist[i] = newdist[i] = INF;
solve(0);
return (ans == INF ? -1 : ans);
}
