#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, A = 0, G = 0, C = 0, T = 0;
  char s[260];
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
    if (s[i] == 'A') A++;
    if (s[i] == 'C') C++;
    if (s[i] == 'G') G++;
    if (s[i] == 'T') T++;
  }
  if (n % 4 > 0 || A > n / 4 || C > n / 4 || G > n / 4 || T > n / 4)
    cout << "===";
  else {
    for (int i = 0; i < n; i++) {
      if (s[i] == '?') {
        if (A < n / 4) {
          s[i] = 'A';
          A++;
          continue;
        }
        if (C < n / 4) {
          s[i] = 'C';
          C++;
          continue;
        }
        if (G < n / 4) {
          s[i] = 'G';
          G++;
          continue;
        }
        if (T < n / 4) {
          s[i] = 'T';
          T++;
          continue;
        }
      }
    }
    for (int i = 0; i < n; i++) cout << s[i];
  }
  return 0;
}
