#include <bits/stdc++.h>
using namespace std;
vector<int> v;
int main() {
  long long int i, j, k, cs, t;
  cin >> t;
  cin >> k;
  int A[10][10] = {
      {-1},    {-1},       {2, -1}, {3, -1},          {2, 2, 3, -1},
      {5, -1}, {5, 3, -1}, {7, -1}, {7, 2, 2, 2, -1}, {7, 3, 3, 2, -1}};
  while (k) {
    i = k % 10;
    for (j = 0;; j++) {
      if (A[i][j] == -1) break;
      v.push_back(A[i][j]);
    }
    k /= 10;
  }
  sort(v.begin(), v.end());
  reverse(v.begin(), v.end());
  for (i = 0; i < v.size(); i++) cout << v[i];
  cout << endl;
  return 0;
}
