#include <bits/stdc++.h>
using namespace std;
int n, need, cnt[4] = {};
string s;
vector<char> v;
int main() {
  cin >> n;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  int need = n / 4;
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A')
      ++cnt[0];
    else if (s[i] == 'C')
      ++cnt[1];
    else if (s[i] == 'G')
      ++cnt[2];
    else if (s[i] == 'T')
      ++cnt[3];
  }
  for (int i = 0; i < 4; i++) {
    if (cnt[i] > need) {
      cout << "===";
      return 0;
    }
  }
  for (int i = 0; i < n; i++) {
    if (s[i] == '?') {
      if (cnt[0] < need) {
        ++cnt[0];
        s[i] = 'A';
      } else if (cnt[1] < need) {
        ++cnt[1];
        s[i] = 'C';
      } else if (cnt[2] < need) {
        ++cnt[2];
        s[i] = 'G';
      } else {
        ++cnt[3];
        s[i] = 'T';
      }
    }
  }
  cout << s << endl;
  return 0;
}
