#include <bits/stdc++.h>
using namespace std;
int n;
string str;
int num[1005];
int main() {
  cin >> n;
  cin >> str;
  for (int i = 0; i < n; i++) {
    num[int(str[i])]++;
  }
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  if (num[int('A')] > n / 4 || num[int('G')] > n / 4 || num[int('C')] > n / 4 ||
      num[int('T')] > n / 4) {
    cout << "===";
    return 0;
  }
  for (int i = 0; i < str.length(); i++) {
    if (str[i] == '?') {
      if (num[int('A')] < n / 4) {
        num[int('A')]++;
        cout << 'A';
      } else if (num[int('G')] < n / 4) {
        num[int('G')]++;
        cout << 'G';
      } else if (num[int('C')] < n / 4) {
        num[int('C')]++;
        cout << 'C';
      } else if (num[int('T')] < n / 4) {
        num[int('T')]++;
        cout << 'T';
      } else {
        cout << "===";
      }
    } else {
      cout << str[i];
    }
  }
  return 0;
}
