#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===\n";
    return 0;
  }
  int a = 0, c = 0, g = 0, t = 0;
  int target = n / 4;
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A') {
      a++;
    }
    if (s[i] == 'C') c++;
    if (s[i] == 'G') g++;
    if (s[i] == 'T') t++;
  }
  a = target - a;
  c = target - c;
  g = target - g;
  t = target - t;
  if (a < 0 || c < 0 || g < 0 || t < 0) {
    cout << "===\n";
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (s[i] == '?') {
      if (a) {
        s[i] = 'A';
        a--;
        continue;
      }
      if (c) {
        s[i] = 'C';
        c--;
        continue;
      }
      if (g) {
        s[i] = 'G';
        g--;
        continue;
      }
      if (t) {
        s[i] = 'T';
        t--;
        continue;
      }
    }
  }
  cout << s << endl;
  return 0;
}
