//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
int n;
ll d[500500];
int c[500500];
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	cin>>n;
	for(int i=1;i<=n;i++)
		cin>>d[i];
	for(int i=2;i<=n;i++)
		cin>>c[i];
	ll tot=0,mn=1ll*inf*inf;
	for(int i=1;i<=n;i++)
	{
		tot+=abs(d[i]);
		mn=min(mn,abs(d[i]));
	}
	int ok=1;
	for(int i=2;i<=n;i++)
		if(d[i]*d[c[i]]>0)
			ok=0;
	if(!ok) tot-=mn*2;
	cout<<tot<<endl;
	return 0;
}