#include <bits/stdc++.h>
int main() {
  static char s[256];
  int n, i, ca, cc, cg, ct, c1, c2, c3, c4;
  scanf("%d%s", &n, s);
  if (n % 4) {
    printf("===\n");
    return 0;
  }
  ca = cc = cg = ct = 0;
  for (i = 0; i < n; i++)
    if (s[i] == 'A')
      ca++;
    else if (s[i] == 'C')
      cc++;
    else if (s[i] == 'G')
      cg++;
    else if (s[i] == 'T')
      ct++;
  if (ca > n / 4 || cc > n / 4 || cg > n / 4 || ct > n / 4) {
    printf("===\n");
    return 0;
  }
  c1 = (n / 4) - ca;
  c2 = (n / 4) - cc;
  c3 = (n / 4) - cg;
  c4 = (n / 4) - ct;
  for (i = 0; i < n; i++)
    if (s[i] == '?' && c1-- > 0) s[i] = 'A';
  for (i = 0; i < n; i++)
    if (s[i] == '?' && c2-- > 0) s[i] = 'C';
  for (i = 0; i < n; i++)
    if (s[i] == '?' && c3-- > 0) s[i] = 'G';
  for (i = 0; i < n; i++)
    if (s[i] == '?' && c4-- > 0) s[i] = 'T';
  printf("%s\n", s);
  return 0;
}
