02. The Matrix

#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

bool isPrime(int n) {
    for (int i = 2; i <= sqrt(n); i++) {
        if (n % i == 0) {
            return false;
        }
    }
    return true;
}

int main() {
    int n;
    cin >> n;

    vector<vector<int>> numbers(n, vector<int>(n));

    for (int r = 0; r < n; r++) {
        for (int c = 0; c < n; c++) {
            cin >> numbers[r][c];
        }
    }

    int startCol = 1, finalCol = n - 1, sum = 0;

    for (int r = n - 1; r > n / 2; r--) {
        for (int c = startCol; c < finalCol; c++) {
            if (isPrime(numbers[r][c])) {
                sum += numbers[r][c];
            }
        }
        startCol++;
        finalCol--;
    }

    cout << sum << endl;
    return 0;
}