#include <cstdio>
#include <algorithm>
#include <bitset>
#include <vector>
#include <set>
#include <cstring>
typedef long long LL;
typedef std::pair<int, int> pii;
typedef std::pair<LL, LL> pll;
#define MP std::make_pair
#define fi first 
#define se second 
int read()
{
	int s = 0, f = 1;
	char c = getchar();
	while (!(c >= '0' && c <= '9'))
		f ^= c == '-', c = getchar();
	while (c >= '0' && c <= '9')
		s = s * 10 + (c - '0'), c = getchar();
	return f ? s : -s;
}
const int MAXN = 400005, INF = 2e9;
int n, a[MAXN], f[MAXN][3][2];
std::vector<int> e[MAXN];
void dfs(int x, int fat)
{
	int ap = 0, bp = 0, dp = -INF;
	int am = 0, bm = 0, dm = -INF;
	for (int y : e[x])
	{
		dfs(y, x);
		ap += std::max({f[y][0][0] - a[y], f[y][1][0], f[y][2][0]});
		am += std::max({f[y][0][0] + a[y], f[y][1][0], f[y][2][0]});
		bp += std::max(f[y][0][0] - a[y], f[y][1][0]);
		bm += std::max(f[y][0][0] + a[y], f[y][1][0]);
		dp = std::max(dp, std::max(f[y][1][1], f[y][2][1]) - std::max({f[y][0][0] - a[y], f[y][1][0], f[y][2][0]}));
		dm = std::max(dp, std::max(f[y][1][1], f[y][2][1]) - std::max({f[y][0][0] + a[y], f[y][1][0], f[y][2][0]}));
	}
	f[x][0][0] = std::max(ap, am);
	f[x][1][0] = std::max(ap + dp, am + dm);
	f[x][1][1] = std::max(ap + dp - a[fat], am + dm + a[fat]);
	f[x][2][0] = std::max(bp + a[x], bm - a[x]);
	f[x][2][1] = std::max(bp + a[x] - a[fat], bm - a[x] + a[fat]);
}
int main()
{
	n = read();
	for (int i = 1; i <= n; i++)
		a[i] = read();
	for (int i = 2; i <= n; i++)
		e[read()].push_back(i);
	dfs(1, 0);
	printf("%d\n", std::max(f[1][1][0], f[1][2][0]));
	return 0;
}