#include <bits/stdc++.h>
using namespace std;
int main() {
  int x, i, k = 0, n[4] = {0}, s = 0, p, m;
  cin >> x;
  char str[x + 1];
  cin >> str;
  for (i = 0; i < x; i++) {
    if (str[i] == 'A')
      n[0]++;
    else if (str[i] == 'C')
      n[1]++;
    else if (str[i] == 'G')
      n[2]++;
    else if (str[i] == 'T')
      n[3]++;
    else if (str[i] == '?')
      k++;
  }
  p = x / 4;
  m = *max_element(n, n + 4);
  if (x % 4 != 0 || m > p)
    cout << "===";
  else {
    for (i = 0; i <= 3; i++) s = s + p - n[i];
    if (s == k) {
      for (i = 0; i < x; i++) {
        if (str[i] == '?') {
          if (p - n[0] > 0) {
            cout << 'A';
            n[0]++;
          } else if ((p - n[1]) > 0) {
            cout << 'C';
            n[1]++;
          } else if (p - n[2] > 0) {
            cout << 'G';
            n[2]++;
          } else if (p - n[3] > 0) {
            cout << 'T';
            n[3]++;
          }
        } else
          cout << str[i];
      }
    }
  }
}
