#include <bits/stdc++.h>
int main() {
  int n, i, j, a = 0, g = 0, c = 0, t = 0, x;
  char s[256];
  scanf("%d", &n);
  scanf("%s", s);
  if (n % 4 != 0)
    printf("===");
  else {
    for (i = 0; i < n; i++) {
      if (s[i] == 'A')
        a++;
      else if (s[i] == 'G')
        g++;
      else if (s[i] == 'C')
        c++;
      else if (s[i] == 'T')
        t++;
      if (a > n / 4 | g > n / 4 | c > n / 4 | t > n / 4) {
        printf("===");
        exit(0);
      }
    }
    x = a + g + c + t;
    if (x == n)
      printf("%s", s);
    else {
      for (i = 0; i < n; i++) {
        if (s[i] == '?') {
          if (a < n / 4) {
            s[i] = 'A';
            a++;
          } else if (g < n / 4) {
            s[i] = 'G';
            g++;
          } else if (c < n / 4) {
            s[i] = 'C';
            c++;
          } else {
            s[i] = 'T';
            t++;
          }
        }
      }
      printf("%s", s);
    }
  }
}
