#include <bits/stdc++.h>
using namespace std;
int main() {
  string s, t = "AGCT";
  int n, i, j, a[4];
  memset(a, 0, sizeof(a));
  cin >> n >> s;
  for (i = 0; i < n; i++) {
    if (s[i] == 'A') a[0]++;
    if (s[i] == 'G') a[1]++;
    if (s[i] == 'C') a[2]++;
    if (s[i] == 'T') a[3]++;
  }
  if ((n % 4 != 0) or (a[0] > (n / 4)) or (a[1] > (n / 4)) or
      (a[2] > (n / 4)) or (a[3] > (n / 4))) {
    cout << "===";
    return 0;
  }
  for (i = 0; i < n; i++) {
    if (s[i] == '?') {
      for (j = 0; j <= 3; j++) {
        if (a[j] < n / 4) {
          s[i] = t[j];
          a[j]++;
          break;
        }
      }
    }
  }
  cout << s;
  return 0;
}
