#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a[4] = {0};
  string s;
  cin >> n >> s;
  if (n % 4)
    cout << "===";
  else {
    string ans = s, x = "";
    for (int i = 0; i < n; i++) {
      if (s[i] == 'A')
        a[0]++;
      else if (s[i] == 'C')
        a[1]++;
      else if (s[i] == 'G')
        a[2]++;
      else if (s[i] == 'T')
        a[3]++;
    }
    for (int i = 0; i < 4; i++) {
      if (a[i] > n / 4) {
        ans = "===";
        break;
      }
    }
    if (ans != "===") {
      x.insert(0, n / 4 - a[0], 'A');
      x.insert(0, n / 4 - a[1], 'C');
      x.insert(0, n / 4 - a[2], 'G');
      x.insert(0, n / 4 - a[3], 'T');
      for (int i = 0; i < n; i++) {
        if (s[i] == '?') {
          s[i] = x[0];
          x.erase(0, 1);
        }
      }
      ans = s;
    }
    cout << ans;
  }
  return 0;
}
