#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main () {
	int N, X;
	cin >> N >>X;
	std::vector<int> P(N);
	for (int i = 1; i < N; i ++) {
		cin >> P[i];
		P[i] --;
	}
	P[0] = -1;
	vector<vector<int>> gr(N);
	for (int i = 1; i < N; i ++) {
		gr[P[i]].push_back(i);
	}
	vector<int> C(N, 0), S(N, 0);
	for (int i = 1; i < N; i ++) {
		cin >> C[i] >> S[i];
	}
	int ss = accumulate(S.begin(), S.end(), 0);
	vector dp(N, vector(ss + 1, (ll)1e18));
	vector siz(N, 0);
	vector<ll> nxt;
	for (int u = N-1; u >= 0; u --) {
		dp[u][0] = 0;
		for (int i = 1; i <= S[u]; i ++) dp[u][i] = C[u];
		siz[u] = S[u] + 1;
		nxt = dp[u];
		for (int v : gr[u]) {
			for (int i = S[u]; i < siz[u]; i ++) {
				for (int j = S[v]; j < siz[v]; j ++) {
					nxt[i + j] = min(nxt[i + j], dp[u][i] + dp[u][j]);
				}
			}
			for (int i = siz[u] + siz[v] - 1; i >= 0; i --) {
				nxt[i] = min(nxt[i], nxt[i+1]);
			}
			swap(dp[u], nxt);
			siz[u] = siz[u] + siz[v] - 1;
		}
	}
	cout << dp[0][X] << endl;
}