#include<bits/stdc++.h>
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define repi(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
typedef long long ll;
using namespace std;

int main(){
  ios::sync_with_stdio(0);
  cin.tie(0);

  ll n;
  cin >> n;
  ll p[n];
  ll k = 1;
  rep(i,n){
    cin >> p[i];
    k *= p[i];
  }
  ll dig;
  ll sum = 0;
  goto keisan;
  keisan:
  while(k){
    dig = k % 10;
    sum = sum + dig;
    k = k / 10;
  }

  int a = to_string(sum).length();
  if(a!=1){
    k = sum;
    sum = 0;
    goto keisan;
  }else{
    cout << sum << endl;
    return 0;
  }
}