#include <bits/stdc++.h>
using namespace std;
string s;
int n;
int A[10], B[10];
int main() {
  A[0] = 2;
  A[1] = 3;
  A[2] = 5;
  A[3] = 7;
  cin >> n;
  cin >> s;
  for (int i = 0; i < s.size(); i++) {
    int a = s[i] - '0';
    for (int j = 2; j <= a; j++) {
      int x = j;
      for (int k = 0; k < 4; k++) {
        while (x % A[k] == 0) B[k]++, x /= A[k];
      }
    }
  }
  vector<int> ans;
  for (int i = 3; i >= 0; i--) {
    int num = B[i];
    for (int t = 0; t < num; t++) ans.push_back(A[i]);
    for (int j = 0; j < 4; j++) {
      int a = A[j];
      int cnt = 0;
      for (int t = 1; t <= A[i]; t++) {
        int x = t;
        while (x % a == 0) x /= a, cnt++;
      }
      B[j] -= cnt * num;
    }
  }
  sort((ans).begin(), (ans).end());
  reverse((ans).begin(), (ans).end());
  for (int i = 0; i < ans.size(); i++) cout << ans[i];
  cout << '\n';
}
