#include <bits/stdc++.h>
void merge(int arr[], int l, int m, int r) {
  int i, j, k;
  int n1 = m - l + 1;
  int n2 = r - m;
  int L[n1], R[n2];
  for (i = 0; i < n1; i++) L[i] = arr[l + i];
  for (j = 0; j < n2; j++) R[j] = arr[m + 1 + j];
  i = 0;
  j = 0;
  k = l;
  while (i < n1 && j < n2) {
    if (L[i] <= R[j]) {
      arr[k] = L[i];
      i++;
    } else {
      arr[k] = R[j];
      j++;
    }
    k++;
  }
  while (i < n1) {
    arr[k] = L[i];
    i++;
    k++;
  }
  while (j < n2) {
    arr[k] = R[j];
    j++;
    k++;
  }
}
void sort(int arr[], int l, int r) {
  if (l < r) {
    int m = l + (r - l) / 2;
    sort(arr, l, m);
    sort(arr, m + 1, r);
    merge(arr, l, m, r);
  }
}
int main() {
  int n;
  scanf("%d", &n);
  long long int m;
  scanf("%lld", &m);
  int arr[n];
  long long int flag = m, k = 0;
  while (flag != 0) {
    arr[k++] = flag % 10;
    flag /= 10;
  }
  int temp[60], j = 0, count = 0;
  for (int i = 0; i < n; i++) {
    if (arr[i] == 2) {
      temp[j++] = 2;
      count++;
    }
    if (arr[i] == 3) {
      temp[j++] = 3;
      count++;
    }
    if (arr[i] == 4) {
      temp[j++] = 3;
      temp[j++] = 2;
      temp[j++] = 2;
      count += 3;
    }
    if (arr[i] == 5) {
      temp[j++] = 5;
      count++;
    }
    if (arr[i] == 6) {
      temp[j++] = 5;
      temp[j++] = 3;
      count += 2;
    }
    if (arr[i] == 7) {
      temp[j++] = 7;
      count++;
    }
    if (arr[i] == 8) {
      temp[j++] = 7;
      temp[j++] = 2;
      temp[j++] = 2;
      temp[j++] = 2;
      count += 4;
    }
    if (arr[i] == 9) {
      temp[j++] = 7;
      temp[j++] = 3;
      temp[j++] = 3;
      temp[j++] = 2;
      count += 4;
    }
  }
  sort(temp, 0, count - 1);
  for (int i = count - 1; i >= 0; i--) printf("%d", temp[i]);
}
