#include <bits/stdc++.h>
using namespace std;
int main() {
  char s[260];
  int a;
  int b;
  int c;
  int d;
  int n;
  while (~scanf("%d", &n)) {
    getchar();
    gets(s);
    if (n % 4 != 0) {
      printf("===\n");
      continue;
    }
    a = 0, b = 0, c = 0, d = 0;
    for (int i = 0; s[i] != 0; i++) {
      if (s[i] == 'A') {
        a++;
      } else if (s[i] == 'G') {
        b++;
      } else if (s[i] == 'C') {
        c++;
      } else if (s[i] == 'T') {
        d++;
      }
    }
    int l = n / 4;
    if (a > l || b > l || c > l || d > l) {
      printf("===\n");
    } else {
      a = l - a;
      b = l - b;
      c = l - c;
      d = l - d;
      for (int i = 0; s[i] != 0; i++) {
        if (s[i] != '?') {
          printf("%c", s[i]);
        } else {
          if (a != 0) {
            printf("A");
            a--;
          } else if (b != 0) {
            printf("G");
            b--;
          } else if (c != 0) {
            printf("C");
            c--;
          } else if (d != 0) {
            printf("T");
            d--;
          }
        }
      }
      printf("\n");
    }
  }
}
