#include <bits/stdc++.h>
#include <boost/multiprecision/cpp_int.hpp>
using namespace std;
namespace mp = boost::multiprecision;

int main(){
    int N;
    cin >> N;
    vector<mp::cpp_int> P(N);
    mp::cpp_int A = 1;
    for (int i = 0; i < N; i++) {
        cin >> P[i];
        A *= P[i];
    }

    while (A >= 10) {
        mp::cpp_int B = 0;
        while (A > 0) {
            B += A%10;
            A /= 10;
        }
        A = B;
    }
    cout << A << endl;
    return 0;
}