#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int n;
    cin >> n;
    long p[n];
    unsigned long long total = 1LL;
    for(int i = 0; i < n; i++) {
        cin >> p[i];
        total *= p[i];
    }
    auto f = [&] (ll c) {
    	ll digit = 0ll;
    	while(c > 0) {
    		digit += c % 10;
    		c = c / 10;
    	}
    	return digit;
	    };
    while(true) {
    	if(total <= 9) {
    		break;
    	}
    	total = f(total);
    }
    cout << total << endl;
}