#include<cstdio>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<vector>
#include<cstring>
#define ios ios::sync_with_stdio(false)
#define R register
#define IL inline
typedef long long LL;

LL n, s, p[9005], dp[9005], a[9005], rd[9005], vis[9005];
std::vector<int> d[9005];

inline void dfs(LL k){
	for(int i = 0; i < d[k].size(); ++i){
		int y = d[k][i];
		if(dp[k] + a[y] < 0){
			//printf("%d\n", y);
			vis[y] = 1;
			continue;
		}
		dfs(y);
		LL P = 0;
		dp[k] += std::max(dp[y],P);
	}
	for(int i = 0; i < d[k].size(); ++i){
		int y = d[k][i];
		if(!vis[y] || dp[k] + a[y] < 0) continue;
		dfs(y);
		LL P = 0;
		dp[k] += std::max(dp[y], P);
	}
}


int main(){
	scanf("%lld%lld", &n, &s);
	for(int i = 2; i <= n; ++i){
		scanf("%lld", &p[i]);
		d[p[i]].push_back(i);
	}
	for(int i = 1; i <= n; ++i){
		scanf("%lld", &a[i]);
		dp[i] = a[i];
	}
	if(dp[1] < -s){
		printf("%lld\n", s);
		return 0;
	}
	dp[1] += s;
	dfs(1);
	printf("%lld\n", dp[1]);
	return 0;
}

具体思路就是两次树形 dp，第一次先把能拿的都拿了，第二次放一个堆将一开始不能拿的从小到大看现在能不能进去拿。结果 WA#60 求负责人 hack。