#include <bits/stdc++.h>
using namespace std;
bool check(string &s, int n) {
  int tam = n / 4;
  int array[] = {0, 0, 0, 0};
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == 'A') {
      array[0]++;
      if (array[0] > tam) {
        return false;
      }
    } else if (s[i] == 'C') {
      array[1]++;
      if (array[1] > tam) {
        return false;
      }
    } else if (s[i] == 'G') {
      array[2]++;
      if (array[2] > tam) {
        return false;
      }
    } else if (s[i] == 'T') {
      array[3]++;
      if (array[3] > tam) {
        return false;
      }
    }
  }
  string res = "";
  int cont = 0;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] != '?') {
      res += s[i];
    } else {
      while (array[cont] == tam) cont++;
      if (cont == 0)
        res += 'A';
      else if (cont == 1)
        res += 'C';
      else if (cont == 2)
        res += 'G';
      else
        res += 'T';
      array[cont]++;
    }
  }
  s = res;
  return true;
}
int main() {
  int n, mamada = 0;
  string s;
  cin >> n;
  cin >> s;
  if (n % 4 == 0) {
    if (check(s, n))
      cout << s << endl;
    else
      cout << "===" << endl;
  } else {
    cout << "===" << endl;
  }
  return 0;
}
