#include <bits/stdc++.h>
#define ll long long
#define endl "\n"
using namespace std;

const int N = 10000000;
bool prime[N + 1];

void sieve()
{
    memset(prime, true, sizeof(prime));
    prime[0] = prime[1] = false;

    for (int i = 2; i * i <= N; ++i)
    {
        if (prime[i])
        {
            for (int j = i * i; j <= N; j += i)
            {
                prime[j] = false;
            }
        }
    }
}

int main() 
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    sieve();
    int n; cin >> n;

    long long a, prefix_sum = 0;
    long long min_val = LLONG_MAX, ans = LLONG_MIN;

    for (int i = 0; i < n; ++i) 
    {
        cin >> a; prefix_sum += a;
        if (prime[i + 1]) ans = max(ans, prefix_sum - min_val);
        if (prime[i + 2]) min_val = min(min_val, prefix_sum);
    }

    cout << ans << endl;

    return 0;
}