include <iostream>

include <cmath>

include <vector>

using namespace std;

// Function to check if a number is prime
bool isPrime(int num) {
if (num <= 1) return false;
if (num == 2 || num == 3) return true;
if (num % 2 == 0 || num % 3 == 0) return false;
for (int i = 5; i * i <= num; i += 6) {
if (num % i == 0 || num % (i + 2) == 0) return false;
}
return true;
}

int main() {
int n;
cin >> n;
vector<int> a(n + 1), primeIndices;

for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    if (isPrime(i)) {
        primeIndices.push_back(i);
    }
}

int maxSum = INT_MIN;
for (int i = 0; i < primeIndices.size(); ++i) {
    for (int j = i; j < primeIndices.size(); ++j) {
        int sum = 0;
        for (int k = primeIndices[i]; k <= primeIndices[j]; ++k) {
            sum += a[k];
        }
        maxSum = max(maxSum, sum);
    }
}

cout << maxSum << endl;
return 0;

}