#include <bits/stdc++.h>
using namespace std;
string itos(int x) {
  stringstream ss;
  ss << x;
  return ss.str();
}
int n, a[5];
string str;
map<char, int> m1;
map<int, char> m2;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> str;
  m1['A'] = 0;
  m1['G'] = 1;
  m1['C'] = 2;
  m1['T'] = 3;
  m1['?'] = 4;
  m2[0] = 'A';
  m2[1] = 'G';
  m2[2] = 'C';
  m2[3] = 'T';
  m2[4] = '?';
  for (auto x : str) a[m1[x]]++;
  if (n % 4 == 0 && *max_element(a, a + 4) <= n / 4) {
    for (auto &x : str) {
      if (m1[x] == 4) {
        auto ptr = min_element(a, a + 4);
        (*ptr)++;
        x = m2[(ptr - a)];
      }
    }
    cout << str << endl;
  } else
    cout << "===" << endl;
  return 0;
}
