#include <bits/stdc++.h>
int main() {
  int i, n;
  char a[300];
  scanf("%d", &n);
  getchar();
  int q = 0, w = 0, e = 0, r = 0, t = 0;
  int j = 0;
  for (i = 1; i <= n; i++) {
    scanf("%c", &a[i]);
    if (a[i] == 'A') q++;
    if (a[i] == 'C') w++;
    if (a[i] == 'G') e++;
    if (a[i] == 'T') r++;
    if (a[i] == '?') t++;
  }
  j = n / 4;
  if (n % 4 == 0) {
    if (j * 4 == n && j >= q && j >= w && j >= e && j >= r) {
      for (i = 1; i <= n; i++) {
        if (a[i] == '?') {
          if (q < j) {
            a[i] = 'A';
            q++;
            continue;
          }
          if (w < j) {
            a[i] = 'C';
            w++;
            continue;
          }
          if (e < j) {
            a[i] = 'G';
            e++;
            continue;
          }
          if (r < j) {
            a[i] = 'T';
            r++;
            continue;
          }
        }
      }
      for (i = 1; i <= n; i++) printf("%c", a[i]);
      printf("\n");
    } else
      printf("===\n");
  } else
    printf("===\n");
  return 0;
}
