#include <bits/stdc++.h>
using namespace std;
int n, cnt[8];
long long x;
void checkmax(int &x, int y) {
  if (x < y) {
    x = y;
  }
}
void modify(int x) {
  switch (x) {
    case 4:
      cnt[2] += 2;
      break;
    case 6:
      cnt[2]++;
      cnt[3]++;
      break;
    case 8:
      cnt[2] += 3;
      break;
    case 9:
      cnt[3] += 2;
      break;
    default:
      cnt[x]++;
      break;
  }
}
void del(int x, int y) {
  switch (x) {
    case 7:
      cnt[7] -= y;
      cnt[5] -= y;
      cnt[3] -= 2 * y;
      cnt[2] -= 4 * y;
      break;
    case 5:
      cnt[5] -= y;
      cnt[3] -= y;
      cnt[2] -= 3 * y;
      break;
    case 3:
      cnt[3] -= y;
      cnt[2] -= y;
      break;
    default:
      cnt[2] -= y;
      break;
  }
}
int main(int argc, char const *argv[]) {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cin >> n >> x;
  while (x) {
    for (int i = x % 10; i >= 2; i--) {
      modify(i);
    }
    x /= 10;
  }
  for (int i = 1; i <= cnt[7]; i++) {
    cout << 7;
  }
  del(7, cnt[7]);
  for (int i = 1; i <= cnt[5]; i++) {
    cout << 5;
  }
  del(5, cnt[5]);
  for (int i = 1; i <= cnt[3]; i++) {
    cout << 3;
  }
  del(3, cnt[3]);
  for (int i = 1; i <= cnt[2]; i++) {
    cout << 2;
  }
  del(2, cnt[2]);
  return 0;
}
