#include <bits/stdc++.h>
using namespace std;
ifstream f("../data.in");
ofstream g("../data.out");
int main() {
  int n;
  cin >> n;
  if (n % 4 != 0) {
    cout << "===" << endl;
    return 0;
  }
  char s[n];
  map<char, int> cN;
  cN['A'] = cN['G'] = cN['C'] = cN['T'] = 0;
  for (int i = 0; i < n; i++) {
    cin >> s[i];
    cN[s[i]] += 1;
  }
  int mx = n / 4;
  if (cN['A'] <= mx && cN['G'] <= mx && cN['C'] <= mx && cN['T'] <= mx) {
    cN['A'] = abs(cN['A'] - mx);
    cN['C'] = abs(cN['C'] - mx);
    cN['G'] = abs(cN['G'] - mx);
    cN['T'] = abs(cN['T'] - mx);
    for (int i = 0; i < n; i++) {
      if (s[i] == '?') {
        if (cN['A']) {
          cout << 'A';
          cN['A']--;
        } else if (cN['C']) {
          cout << 'C';
          cN['C']--;
        } else if (cN['G']) {
          cout << 'G';
          cN['G']--;
        } else if (cN['T']) {
          cout << 'T';
          cN['T']--;
        }
      } else
        cout << s[i];
    }
  } else
    cout << "===" << endl;
  return 0;
}
