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