#include <bits/stdc++.h>
using namespace std;
int max(int a, int b) { return a > b ? a : b; }
int main() {
  int n;
  cin >> n;
  char str[n + 1];
  cin >> str;
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  int a, g, c, t, m;
  a = g = c = t = m = 0;
  for (int i = 0; i < n; i++) {
    if (str[i] == 'A')
      a++;
    else if (str[i] == 'G')
      g++;
    else if (str[i] == 'C')
      c++;
    else if (str[i] == 'T')
      t++;
    else
      m++;
  }
  if (max(max(max(a, g), c), t) > (n / 4)) {
    cout << "===";
    return 0;
  }
  int e = n / 4;
  for (int i = 0; i < n; i++) {
    if (str[i] == '?') {
      if (a < e) {
        str[i] = 'A';
        a++;
      } else if (g < e) {
        str[i] = 'G';
        g++;
      } else if (c < e) {
        str[i] = 'C';
        c++;
      } else {
        str[i] = 'T';
        t++;
      }
    }
  }
  cout << str;
  return 0;
}
