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