#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===" << endl;
    return 0;
  }
  int cnt = 0;
  int tmp = (n / 4);
  int a = tmp, g = tmp, c = tmp, t = tmp;
  for (int i = 0; s[i]; i++) {
    if (s[i] == '?') cnt++;
    if (s[i] == 'A') a--;
    if (s[i] == 'G') g--;
    if (s[i] == 'C') c--;
    if (s[i] == 'T') t--;
  }
  if ((a < 0) || (g < 0) || (c < 0) || (t < 0)) {
    cout << "===" << endl;
    return 0;
  }
  for (int i = 0; s[i]; i++) {
    if (s[i] == '?') {
      if (a > 0) {
        cout << "A";
        a--;
      } else if (g > 0) {
        cout << "G";
        g--;
      } else if (c > 0) {
        cout << "C";
        c--;
      } else if (t > 0) {
        cout << "T";
        t--;
      }
    } else
      cout << s[i];
  }
  cout << endl;
  return 0;
}
