#include <iostream>
#include <vector>
#include <utility>
#include <map>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;

int main() {
    int n;
    cin >> n;
    unsigned long long k = 1;
    for (int i=0; i<n; i++) {
        unsigned long long p;
        cin >> p;
        k *= p;
    }

    long long ans = k;
    while(ans >= 10) {
        k = ans;
        ans = 0;
        while (k > 0) {
            ans += (k % 10);
            k /= 10;
        }
    }
    cout << ans << endl;
}