#include <bits/stdc++.h>
using namespace std;
int k[150];
bool cmp(int a, int b) { return a >= b; }
int main() {
  int n, i, temp, t;
  long long a;
  int number[10][15] = {{0}, {0},    {2}, {3},          {3, 2, 2},
                        {5}, {5, 3}, {7}, {7, 2, 2, 2}, {7, 2, 3, 3}};
  while (scanf("%d", &n) == 1) {
    t = 0;
    memset(k, 0, sizeof(k));
    cin >> a;
    while (a != 0) {
      temp = a % 10;
      if (temp != 0 && temp != 1) {
        for (i = 0; number[temp][i] != 0; i++) {
          k[t] = number[temp][i];
          t++;
        }
      }
      a = a / 10;
    }
    sort(k, k + t, cmp);
    for (i = 0; i < t; i++) printf("%d", k[i]);
    printf("\n");
  }
  return 0;
}
