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