#include <bits/stdc++.h>
using namespace std;
string s;
int cnt[256], n;
int main() {
  cin >> n >> s;
  if (n % 4) {
    cout << "===" << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (s[i] != '?') {
      cnt[s[i]]++;
    }
  }
  int x = n / 4;
  if (cnt['A'] > x || cnt['C'] > x || cnt['G'] > x || cnt['T'] > x) {
    cout << "===" << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (s[i] != '?') {
      cout << s[i];
    } else {
      if (cnt['A']++ < x) {
        cout << 'A';
      } else if (cnt['C']++ < x) {
        cout << 'C';
      } else if (cnt['G']++ < x) {
        cout << 'G';
      } else {
        cout << 'T';
      }
    }
  }
  cout << endl;
  return 0;
}
