#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, Max = 1, a = 0, c = 0, g = 0, t = 0;
  string s;
  cin >> k >> s;
  a = count(s.begin(), s.end(), 'A');
  c = count(s.begin(), s.end(), 'C');
  g = count(s.begin(), s.end(), 'G');
  t = count(s.begin(), s.end(), 'T');
  Max = max(Max, max(max(max(a, c), g), t));
  if (k % 4 != 0 || k / 4 < Max) return cout << "===", 0;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] != '?')
      cout << s[i];
    else if (a < k / 4) {
      cout << 'A';
      a++;
    } else if (c < k / 4) {
      cout << 'C';
      c++;
    } else if (g < k / 4) {
      cout << 'G';
      g++;
    } else {
      cout << 'T';
      t++;
    }
  }
}
