#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	int n, x; cin >> n >> x;
	vector to(n, vector<int>());
	rep2(i, 1, n) {
		int p; cin >> p;
		p--;
		to[p].push_back(i);
	}
	vector<int>c(n), s(n);
	rep2(i, 1, n)cin >> c[i] >> s[i];
	auto dfs = [&](auto &&self, int v, int p = -1)->vector<long long> {
		vector<long long>dp = { 0 };// childonly
		for (auto nv : to[v]) {
			if (p == nv)continue;
			auto sdp = self(self, nv, v);
			vector<long long> ndp(dp.size() + sdp.size() - 1, LINF);
			rep(i, dp.size())rep(j, sdp.size()) {
				chmin(ndp[i + j], dp[i] + sdp[j]);
			}
			dp.swap(ndp);
		}
		// add pare;
		vector<long long>ndp(dp.size() + s[v], LINF);
		ndp[0] = 0;

		rep(i, dp.size())chmin(ndp[i + s[v]], dp[i] + c[v]);
		dp.swap(ndp);

		return dp;
	};
	auto dp = dfs(dfs, 0);
	long long ans = LINF;
	rep2(i, x, dp.size())chmin(ans, dp[i]);
	cout << ans << endl;
	return 0;
}