#include <bits/stdc++.h>
using namespace std;
char a[260];
int na, ng, nc, nt;
int main() {
  int N, num = 0;
  scanf("%d %s", &N, a);
  for (int i = 0; i < N; i++) {
    if (a[i] == '?')
      num++;
    else if (a[i] == 'A')
      na++;
    else if (a[i] == 'T')
      nt++;
    else if (a[i] == 'C')
      nc++;
    else
      ng++;
  }
  int nl = N / 4;
  if (N % 4 || na > nl || nt > nl || nc > nl || ng > nl)
    printf("===\n");
  else {
    for (int i = 0; i < N; i++)
      if (a[i] == '?') {
        if (na < nl) {
          a[i] = 'A';
          na++;
        } else if (nt < nl) {
          a[i] = 'T';
          nt++;
        } else if (nc < nl) {
          a[i] = 'C';
          nc++;
        } else {
          a[i] = 'G';
          ng++;
        }
      }
    cout << a;
  }
  return 0;
}
