#include <bits/stdc++.h>
using namespace std;
char a[105], c[200000];
int main() {
  int m;
  scanf("%d", &m);
  getchar();
  gets(a);
  char ch;
  int flag = 0;
  int i, j = 0;
  int l = strlen(a);
  for (i = 0; i < l; i++) {
    if (a[i] == '0' || a[i] == '1') continue;
    if (a[i] == '2' || a[i] == '3' || a[i] == '5' || a[i] == '7')
      c[flag++] = a[i];
    else if (a[i] == '4') {
      c[flag++] = '2';
      c[flag++] = '2';
      c[flag++] = '3';
    } else if (a[i] == '8') {
      c[flag++] = '2';
      c[flag++] = '2';
      c[flag++] = '2';
      c[flag++] = '7';
    } else if (a[i] == '6') {
      c[flag++] = '3';
      c[flag++] = '5';
    } else if (a[i] == '9') {
      c[flag++] = '3';
      c[flag++] = '3';
      c[flag++] = '2';
      c[flag++] = '7';
    }
  }
  c[flag] = '\0';
  sort(c, c + flag);
  l = strlen(c);
  for (i = l - 1; i >= 0; i--) cout << c[i];
  cout << endl;
  return 0;
}
