#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream fin("asmax.in");
ofstream fout("asmax.out");
#define MAX 16005
vector < int > G[MAX];
int viz[MAX],sm[MAX],a[MAX];
void dfs(int nod)
{
    int k=0;
    viz[nod]=1;
    for (int i = 0; i<G[nod].size(); i++){
        if(!viz[G[nod][i]])
            dfs(G[nod][i]);
        if(sm[G[nod][i]]>0)
            k+=sm[G[nod][i]];
    }
    sm[nod]=a[nod]+k;
}

int main()
{
    int n;
    for (int i = 1; i<=n; i++)
        fin >> a[i];
    dfs(1);
    int mx=(1<<31);
    for (int i = 1; i<=n; i++)
        mx=max(mx,sm[i]);
    fout << mx << "\n";
    return 0;
}