#include <bits/stdc++.h>
using namespace std;
bool cmp(int x, int y) { return x > y; }
int main() {
  int n, Num[4], count = 0, sum = 0, x, flag = 1;
  char s[300], ch;
  scanf("%d", &n);
  getchar();
  memset(Num, 0, sizeof(Num));
  for (int i = 0; i < n; i++) {
    scanf("%c", &s[i]);
    if (s[i] == 'A')
      Num[0]++;
    else if (s[i] == 'G')
      Num[1]++;
    else if (s[i] == 'C')
      Num[2]++;
    else if (s[i] == 'T')
      Num[3]++;
    else
      count++;
  }
  if (n % 4 != 0) {
    printf("===\n");
  } else {
    x = n / 4;
    for (int i = 0; i < 4; i++) {
      if (Num[i] > x) {
        flag = 0;
        break;
      }
    }
    if (flag) {
      for (int j = 0; j < n; j++) {
        if (s[j] != '?')
          printf("%c", s[j]);
        else {
          if (x > Num[0]) {
            printf("A");
            Num[0]++;
          } else if (x == Num[0] && x > Num[1]) {
            printf("G");
            Num[1]++;
          } else if (x == Num[0] && x == Num[1] && x > Num[2]) {
            printf("C");
            Num[2]++;
          } else if (x == Num[0] && x == Num[1] && x == Num[2] && x > Num[3]) {
            printf("T");
            Num[3]++;
          }
        }
      }
      printf("\n");
    } else
      printf("===\n");
  }
  return 0;
}
