#include <bits/stdc++.h>
using namespace std;
int n;
string s;
int a[5], c[5];
map<int, char> mp;
int main() {
  ios::sync_with_stdio(false);
  cin >> n;
  if (n % 4) cout << "===", exit(0);
  cin >> s;
  mp[0] = 'A', mp[1] = 'G', mp[2] = 'C';
  mp[3] = 'T';
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A')
      a[0]++;
    else if (s[i] == 'G')
      a[1]++;
    else if (s[i] == 'C')
      a[2]++;
    else if (s[i] == 'T')
      a[3]++;
    else
      a[4]++;
  }
  int mx = max(max(a[0], a[1]), max(a[2], a[3]));
  int ned = 4 * mx - a[0] - a[1] - a[2] - a[3];
  if (a[4] < ned) cout << "===", exit(0);
  for (int i = 0; i < 5; i++) c[i] = mx - a[i], c[i] += (a[4] - ned) / 4;
  for (int i = 0; i < n; i++) {
    if (s[i] == '?') {
      for (int j = 0; j < 4; j++) {
        if (c[j] > 0) {
          c[j]--;
          s[i] = mp[j];
          break;
        }
      }
    }
  }
  cout << s << endl;
}
