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