#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int a = 0, c = 0, g = 0, t = 0;
  int n;
  cin >> n;
  string s;
  cin >> 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');
  for (int i = 0; i < n; i++) {
    if (s[i] == '?') {
      if (a < max(a, max(c, max(g, t)))) {
        s[i] = 'A';
        a++;
      } else if (c < max(a, max(c, max(g, t)))) {
        s[i] = 'C';
        c++;
      } else if (g < max(a, max(c, max(g, t)))) {
        s[i] = 'G';
        g++;
      } else if (t < max(a, max(c, max(g, t)))) {
        s[i] = 'T';
        t++;
      } else {
        s[i] = 'A';
        a++;
      }
    }
  }
  if (a == c && a == g && a == t) {
    cout << s << endl;
  } else {
    cout << "===\n";
  }
  return 0;
}
