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