#include <bits/stdc++.h>
using namespace std;
char s[10000];
int main() {
  int n;
  scanf("%d", &n);
  scanf("%s", s);
  int A = 0, C = 0, G = 0, T = 0;
  for (int i = 0; i < int(n); i++) {
    if (s[i] == 'A')
      A++;
    else if (s[i] == 'C')
      C++;
    else if (s[i] == 'G')
      G++;
    else if (s[i] == 'T')
      T++;
  }
  if (n % 4 != 0)
    printf("===\n");
  else {
    if (A > n / 4 || C > n / 4 || G > n / 4 || T > n / 4)
      printf("===\n");
    else {
      queue<char> q;
      for (int i = 0; i < int(n / 4 - A); i++) q.push('A');
      for (int i = 0; i < int(n / 4 - C); i++) q.push('C');
      for (int i = 0; i < int(n / 4 - G); i++) q.push('G');
      for (int i = 0; i < int(n / 4 - T); i++) q.push('T');
      for (int i = 0; i < int(n); i++) {
        if (s[i] == '?') {
          s[i] = q.front();
          q.pop();
        }
      }
      printf("%s\n", s);
    }
  }
}
