#include <bits/stdc++.h>
using namespace std;
const int maxn = 6e5 + 5;
const long long mod = 10000000000000007;
const long long nary = 9;
long long a;
int ans[100], n;
int main() {
  while (scanf("%d%I64d", &n, &a) != EOF) {
    n = 0;
    while (a > 0) {
      int d = (int)(a % 10);
      a /= (long long)10;
      if (d == 9) {
        d -= 2;
        ans[++n] = 3;
        ans[++n] = 3;
        ans[++n] = 2;
      }
      if (d == 8) {
        d--;
        ans[++n] = 2;
        ans[++n] = 2;
        ans[++n] = 2;
      }
      if (d == 6) {
        d--;
        ans[++n] = 3;
      }
      if (d == 4) {
        d--;
        ans[++n] = 2;
        ans[++n] = 2;
      }
      if (d > 1) ans[++n] = d;
    }
    sort(ans + 1, ans + n + 1);
    for (int i = n; i > 0; i--) printf("%d", ans[i]);
    printf("\n");
  }
  return 0;
}
