#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;
 
  vector<string> p(n);
  rep(i,n) cin >> p[i];
  string k = p[0];
  for (int i = 1; i < n; i++) {
    ll sum = 0;
    for (int j = 0; j < sz(k); j++) {
      ll a = k[j] - '0';
      for (int t = 0; t < sz(p[i]); t++) {
        ll b = p[i][t] - '0';
        sum += a * b;
      }
    }
    k = to_string(sum);
  }

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