#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===\n";
    return 0;
  }
  int k = n / 4;
  int a[4] = {0, 0, 0, 0};
  char c[4] = {'A', 'C', 'G', 'T'};
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A') a[0]++;
    if (s[i] == 'C') a[1]++;
    if (s[i] == 'G') a[2]++;
    if (s[i] == 'T') a[3]++;
  }
  for (int i = 0; i < 4; i++) {
    if (a[i] > k) {
      cout << "===\n";
      return 0;
    }
    a[i] = k - a[i];
  }
  for (int i = 0; i < n; i++) {
    if (s[i] == '?') {
      int j;
      for (j = 0; a[j] == 0 && j < 4; j++)
        ;
      s[i] = c[j];
      a[j]--;
    }
  }
  cout << s << "\n";
}
