#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long ll;
int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N;
  ll P, K = 1;
  cin >> N;
  REP(i, N){
    cin >> P;
    K *= P;
  }
  while(K > 9){
    int s = (int)log10(K) + 1;
    ll tmp = 0;
    REP(i, s){
      tmp += K % 10;
      K /= 10;
    }
    K = tmp;
  }
  cout << K << endl;
}