#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define F(i,j,k) f[i][j][k]
const ll INF=1e18,N=400005;
ll a[N],f[N][3][2];
vector<int>go[N];
ll mx(ll f[2]) {return max(f[0],f[1]);}
inline void dfs(int u)
{
    F(u,0,0)=a[u],F(u,0,1)=-a[u];
    F(u,1,0)=F(u,1,1)=-INF;
    F(u,2,0)=F(u,2,1)=0;
    for(int v:go[u])
    {
        dfs(v);
        for(int i:{0,1})
        {
            F(u,0,i)+=max(mx(f[v][1]),mx(f[v][2])+a[v]*(i?1:-1));
            F(u,1,i)=max(F(u,1,i)+max(max(mx(f[v][0]),mx(f[v][1])),mx(f[v][2])+a[v]*(i?1:-1)),F(u,2,i)+max(max(F(v,0,0),F(v,1,0))-a[u],max(F(v,0,1),F(v,1,1))+a[u]));
            F(u,2,i)+=max(max(mx(f[v][0]),mx(f[v][1])),mx(f[v][2])+a[v]*(i?1:-1));
        }
    }
}
inline int read()
{
    int ret=0,f=1; char ch=getchar();
    while(!isdigit(ch)) {if(ch=='-') f=-1; ch=getchar();}
    while(isdigit(ch)) ret=ret*10+ch-'0',ch=getchar();
    return ret;
}
int main()
{
    int n; n=read(); for(int i=1;i<=n;++i) a[i]=read();
    for(int i=2;i<=n;++i) go[read()].push_back(i); dfs(1);
    cout<<max(mx(f[1][0]),mx(f[1][1]))<<endl;
    return 0;
}