#include <bits/stdc++.h>
int main() {
  int n, a, c, g, t;
  char s[300];
  scanf("%d%s", &n, s);
  if (n % 4)
    printf("===\n");
  else {
    a = c = g = t = 0;
    int cnt = n / 4;
    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++;
    }
    if (a > cnt || c > cnt || g > cnt || t > cnt)
      printf("===\n");
    else {
      a = cnt - a;
      c = cnt - c;
      g = cnt - g;
      t = cnt - t;
      for (int i = 0; i < n; i++) {
        if (s[i] == '?') {
          if (a) {
            s[i] = 'A';
            a--;
          } else if (c) {
            s[i] = 'C';
            c--;
          } else if (g) {
            s[i] = 'G';
            g--;
          } else {
            s[i] = 'T';
            t--;
          }
        }
        printf("%c", s[i]);
      }
      printf("\n");
    }
  }
  return 0;
}
