#include <bits/stdc++.h>
using namespace std;
string s;
int mark[100];
vector<int> v, va, vb;
void factor(int x) {
  for (int i = 0; i < v.size(); i++) {
    if (x % v[i] == 0) {
      while (x % v[i] == 0) {
        va.push_back(v[i]);
        x /= v[i];
        mark[v[i]]++;
      }
    }
  }
}
void factor2(int x) {
  for (int i = 0; i < v.size(); i++) {
    if (x % v[i] == 0) {
      while (x % v[i] == 0) {
        mark[v[i]]--;
        x /= v[i];
      }
    }
  }
}
int main() {
  int n, m, i, j, k, x, y, z;
  cin >> n >> s;
  v.push_back(2);
  v.push_back(3);
  v.push_back(5);
  v.push_back(7);
  for (i = 0; i < s.size(); i++) {
    x = s[i] - '0';
    if (x > 1) {
      for (j = 2; j <= x; j++) factor(j);
    }
  }
  sort(va.begin(), va.end());
  for (i = va.size() - 1; i >= 0; i--) {
    if (mark[va[i]] > 0) {
      vb.push_back(va[i]);
      for (j = 2; j <= va[i]; j++) {
        factor2(j);
      }
    }
  }
  for (i = 0; i < vb.size(); i++) cout << vb[i];
  cout << endl;
  return 0;
}
