#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int a = 0, g = 0, c = 0, t = 0;
  int i, j;
  char str[10000];
  cin >> n;
  cin >> str;
  if (n % 4 == 0) {
    for (i = 0; str[i] != '\0'; i++) {
      if (str[i] == 'A') {
        a++;
      } else if (str[i] == 'G') {
        g++;
      } else if (str[i] == 'T') {
        t++;
      } else if (str[i] == 'C') {
        c++;
      }
    }
    int p = max(a, max(g, max(t, c)));
    if (p <= n / 4) {
      for (i = 0; str[i] != '\0'; i++) {
        if (str[i] == '?') {
          if (a < n / 4) {
            str[i] = 'A';
            a++;
          } else if (g < n / 4) {
            str[i] = 'G';
            g++;
          } else if (t < n / 4) {
            str[i] = 'T';
            t++;
          } else if (c < n / 4) {
            str[i] = 'C';
            c++;
          }
        }
      }
      cout << str << endl;
      return 0;
    } else {
      cout << "===" << endl;
    }
  } else {
    cout << "===" << endl;
    return 0;
  }
  return 0;
}
