#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i, x, j;
  cin >> n;
  if (n % 4 != 0)
    cout << "===";
  else {
    vector<int> v(122, 0), vec(4);
    vector<char> s(n), s1{'A', 'G', 'C', 'T'};
    for (i = 0; i < n; i++) {
      cin >> s[i];
      v[s[i]]++;
    }
    vec[0] = v[65];
    vec[2] = v[67];
    vec[1] = v[71];
    vec[3] = v[84];
    x = n / 4;
    if (vec[0] > x || vec[1] > x || vec[2] > x || vec[3] > x)
      cout << "===";
    else {
      for (i = 0; i < 4; i++)
        while (count(s.begin(), s.end(), s1[i]) != x)
          for (j = 0; j < s.size(); j++)
            if (s[j] == '?') {
              s[j] = s1[i];
              break;
            }
      for (i = 0; i < n; i++) cout << s[i];
    }
  }
  return 0;
}
