#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  map<char, int> freq;
  string types = "ACGT";
  for (int i = 0; i < n; i++) {
    if (s[i] != '?') freq[s[i]]++;
  }
  for (int i = 0; i < n; i++)
    if (s[i] == '?') {
      int maxFreq = -1;
      bool isEqual = true;
      for (int j = 0; j < 4; j++) {
        int curFreq = freq[types[j]];
        if (maxFreq == -1 || maxFreq < curFreq) {
          maxFreq = curFreq;
        }
        if (curFreq != maxFreq) {
          isEqual = false;
        }
      }
      if (isEqual) {
        s[i] = 'A';
        freq['A']++;
      } else {
        for (int j = 0; j < 4; j++) {
          if (freq[types[j]] < maxFreq) {
            s[i] = types[j];
            freq[types[j]]++;
            break;
          }
        }
      }
    }
  map<char, int> newFreq;
  for (int i = 0; i < n; i++) newFreq[s[i]]++;
  int value = -1;
  bool isValid = true;
  for (int i = 0; i < 4; i++) {
    int f = newFreq[types[i]];
    if (value == -1) value = f;
    if (f != value) {
      isValid = false;
    }
  }
  if (isValid)
    cout << s << "\n";
  else
    cout << "==="
         << "\n";
}
