#include<bits/stdc++.h>
using namespace std;

int main(){
	int N,X;
	cin >> N >> X;
	vector<vector<int>> G(N);
	for(int i=1;i<N;i++){
		int p;
		cin >> p;
		G[p-1].emplace_back(i);
	}
	vector<long long> c(N,0LL);
	vector<int> s(N,0);
	for(int i=1;i<N;i++) cin >> c[i] >> s[i];
	function<vector<long long>(int)> dfs=[&](int v){
		vector<long long> res(s[v]+1,1000000000000000000LL);
		res[s[v]]=c[v];
		for(int nv : G[v]){
			vector<long long> res2=dfs(nv);
			vector<long long> res3((int)(res.size())+(int)(res2.size())-1,1000000000000000000LL);
			for(int i=0;i<(int)(res.size());i++) for(int j=0;j<(int)(res2.size());j++) res3[i+j]=min(res3[i+j],res[i]+res2[j]);
			swap(res,res3);
		}
		res[0]=0;
		return res;
	};
	vector<long long> dp=dfs(0);
	long long ans=1000000000000000000LL;
	for(int i=X;i<(int)(dp.size());i++) ans=min(ans,dp[i]);
	cout << ans << '\n';
}