#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  string s;
  cin >> n >> s;
  bool ok = n % 4 == 0;
  int t = n / 4;
  map<char, int> m;
  for (auto c : "ACGT")
    if (c) m[c] = 0;
  for (char c : s) {
    if (c != '?') {
      ++m[c];
      if (m[c] > t) {
        ok = false;
      }
    }
  }
  for (int i = 0; i < n; ++i) {
    if (s[i] == '?') {
      for (auto& p : m) {
        if (p.second < t) {
          s[i] = p.first;
          ++p.second;
          break;
        }
      }
    }
  }
  if (ok) {
    cout << s << endl;
  } else {
    cout << "===" << endl;
  }
  return 0;
}
