#include <bits/stdc++.h>
using namespace std;
int main() {
  int a = 0, c = 0, g = 0, t = 0, flag, n, ex = 0;
  int a1, c1, g1, t1;
  char s[500];
  scanf("%d%*c", &n);
  int div = n / 4;
  gets(s);
  if (n % 4 == 0) {
    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 (s[i] == '?') ex++;
    }
    a1 = div - a;
    c1 = div - c;
    g1 = div - g;
    t1 = div - t;
    if (a1 < 0) a1 = a1 * (-1);
    if (c1 < 0) c1 = c1 * (-1);
    if (g1 < 0) g1 = g1 * (-1);
    if (t1 < 0) t1 = t1 * (-1);
    if (a1 + c1 + g1 + t1 == ex) {
      for (int i = 0; i < n; i++) {
        if (s[i] == '?') {
          if (a != div && a <= div) {
            printf("A");
            a++;
          } else if (c != div && c <= div) {
            printf("C");
            c++;
          } else if (g != div && g <= div) {
            printf("G");
            g++;
          } else if (t != div && t <= div) {
            printf("T");
            t++;
          }
        } else
          printf("%c", s[i]);
      }
    } else {
      printf("===\n");
      return 0;
    }
  } else {
    printf("===\n");
    return 0;
  }
  printf("\n");
  return 0;
}
