#include <bits/stdc++.h>
using namespace std;
int n, a, t, c, g;
char s[1000];
int main() {
  cin >> n;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  for (int i = 0; i < n; ++i) {
    if (s[i] == 'A') a++;
    if (s[i] == 'C') c++;
    if (s[i] == 'G') g++;
    if (s[i] == 'T') t++;
  }
  bool flag = true;
  if (a > n / 4) flag = false;
  if (c > n / 4) flag = false;
  if (t > n / 4) flag = false;
  if (g > n / 4) flag = false;
  if (!flag) {
    cout << "===";
    return 0;
  }
  for (int i = 1; i <= n / 4 - a; ++i) {
    for (int j = 0; j < n; ++j)
      if (s[j] == '?') {
        s[j] = 'A';
        break;
      }
  }
  for (int i = 1; i <= n / 4 - t; ++i) {
    for (int j = 0; j < n; ++j)
      if (s[j] == '?') {
        s[j] = 'T';
        break;
      }
  }
  for (int i = 1; i <= n / 4 - c; ++i) {
    for (int j = 0; j < n; ++j)
      if (s[j] == '?') {
        s[j] = 'C';
        break;
      }
  }
  for (int i = 1; i <= n / 4 - g; ++i) {
    for (int j = 0; j < n; ++j)
      if (s[j] == '?') {
        s[j] = 'G';
        break;
      }
  }
  cout << s << endl;
  return 0;
}
