#include <bits/stdc++.h>
using namespace std;
int n;
char s[256];
int vis[8];
int main() {
  while (~scanf("%d", &n)) {
    scanf("%s", s);
    int len = strlen(s);
    if (n % 4) {
      printf("===\n");
      continue;
    }
    for (int i = 0; i < n; i++) {
      if (s[i] == 'A')
        vis[0]++;
      else if (s[i] == 'C')
        vis[1]++;
      else if (s[i] == 'G')
        vis[2]++;
      else if (s[i] == 'T')
        vis[3]++;
    }
    int ave = n / 4;
    for (int i = 0; i < 4; i++) {
      if (vis[i] > ave) {
        printf("===\n");
        return 0;
      }
    }
    for (int i = 0; i < len; i++) {
      if (s[i] == '?') {
        if (vis[0] < ave) {
          printf("A");
          vis[0]++;
          continue;
        } else if (vis[1] < ave) {
          printf("C");
          vis[1]++;
          continue;
        } else if (vis[2] < ave) {
          printf("G");
          vis[2]++;
          continue;
        } else if (vis[3] < ave) {
          printf("T");
          vis[3]++;
          continue;
        }
      } else
        printf("%c", s[i]);
    }
    printf("\n");
  }
  return 0;
}
