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