#include <iostream>
#include <vector>
using namespace std;
using ll = long long;
int K = 3000;
vector<vector<int>> G(K);
vector<ll> C(K, 0);
vector<int> S(K, 0);
ll inf = (1LL << 60);
vector<vector<ll>> dp(K+1, vector<ll>(K+1, inf));
int dfs(int v, int par) {
	int sub = S[v];
	vector<ll> DP(1, 0);
	for (auto nv : G[v]) {
		if (nv == par) continue;
		int M = dfs(nv, v);
		sub += M;
		vector<ll> ndp(DP.size()+M,inf);
		for (int i = 0;i < DP.size();i++) for (int j = 0;j <= M;j++) {
			if (DP[i] == inf or dp[nv][j] == inf) continue;
			ndp[i+j] = min(ndp[i+j], DP[i]+dp[nv][j]);
		}
		swap(ndp, DP);
	}
	for (int i = 0;i < DP.size();i++) {
		dp[v][i+S[v]] = DP[i] + C[v];
	}
	dp[v][0] = 0;
	return sub;
}
int main() {
	int N, X;cin >> N >> X;
	for (int i = 1;i < N;i++) {
		int a;cin >> a;
		a--;
		G[i].push_back(a);
		G[a].push_back(i);
	}
	for (int i = 1;i < N;i++) cin >> C[i] >> S[i];
	dfs(0, 0);
	ll ans = inf;
	for (int t = X;t <= K;t++) ans = min(ans, dp[0][t]);
	cout << ans << endl;
}