#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s;
  cin >> n;
  cin >> s;
  int A, G, T, C;
  A = G = T = C = 0;
  int fl = n % 4 == 0;
  int mx = n / 4;
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A') A++;
    if (s[i] == 'G') G++;
    if (s[i] == 'T') T++;
    if (s[i] == 'C') C++;
    if (A > mx or T > mx or C > mx or G > mx) fl = 0;
  }
  C = n / 4 - C;
  G = n / 4 - G;
  A = n / 4 - A;
  T = n / 4 - T;
  if (fl) {
    for (int i = 0; i < n; i++) {
      if (s[i] == '?') {
        if (A) {
          cout << 'A';
          A--;
        } else if (T) {
          cout << 'T';
          T--;
        } else if (C) {
          cout << 'C';
          C--;
        } else if (G) {
          cout << 'G';
          G--;
        }
      } else {
        cout << s[i];
      }
    }
    cout << endl;
  } else {
    cout << "===" << endl;
  }
}
