#include <bits/stdc++.h>

using namespace std;

#define MAXN 5005
int n, arr[MAXN], dp[MAXN], res;

bool is_prime(int x){
    if (x == 2) return 1;
    if (x % 2 == 0 || x == 1) return 0;
    int a = sqrt(x);
    for (int i=2; i<=a; i++){
        if (x % i == 0) return 0;
    }
    return 1;
}

int main()
{
    cin >> n;
    int sum = 0;
    for (int i=1; i<=n; i++){
        cin >> arr[i];
        sum += arr[i];
        dp[i] += sum;
    }
    for (int i=1; i<=n; i++){
        for (int j=1; j<i; j++){
            if (is_prime(i - j + 1)){
                res = max(res, dp[i] - dp[j - 1]);
            }
        }
    }
    cout << res << "\n";

}