#include <bits/stdc++.h>
using namespace std;
int n;
string a;
char x[250];
int main() {
  cin >> n >> a;
  int l = 0;
  for (int i = 0; i < a.size(); i++) {
    int d = a[i] - '0';
    if (a[i] == '0' || a[i] == '1') continue;
    if (a[i] == '2' || a[i] == '3' || a[i] == '5' || a[i] == '7')
      x[l++] += a[i];
    else {
      if (d == 4) {
        x[l++] += '3';
        x[l++] += '2';
        x[l++] += '2';
      }
      if (d == 6) {
        x[l++] += '5';
        x[l++] += '3';
      };
      if (d == 8) {
        x[l++] += '7';
        x[l++] += '2';
        x[l++] += '2';
        x[l++] += '2';
      }
      if (d == 9) {
        x[l++] += '7';
        x[l++] += '3';
        x[l++] += '3';
        x[l++] += '2';
      }
    }
  }
  sort(x, x + l);
  reverse(x, x + l);
  cout << x << endl;
  return 0;
}
