#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

int main(){
  int n;
  cin >> n;
  string K;
  ll x = 1;
  rep(i,n) {
    ll p;
    cin >> p;
    x *= p;
  }
  K = to_string(x);

  while (K.size() != 1) {
    ll d = 0;
    rep(i,K.size()) d += K[i] - '0';
    K = to_string(d);
  }
  cout << K << endl;
  return 0;
}