#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18;
const int maxn = 2e5 + 10;
const long long MOD = 1000000007;
const double EPS = 1e-10;
const double Pi = acos(-1.0);
string s;
map<char, int> mp;
int main() {
  int n;
  mp.clear();
  cin >> n;
  cin >> s;
  if (n % 4 != 0) {
    cout << "===" << endl;
    return 0;
  }
  int m = n / 4;
  for (int i = 0; i < n; i++) {
    mp[s[i]]++;
    if (mp[s[i]] > m && s[i] != '?') {
      cout << "===" << endl;
      return 0;
    }
  }
  for (int i = 0; i < n; i++) {
    if (s[i] != '?')
      cout << s[i];
    else {
      if (mp['A'] < m) {
        cout << "A";
        mp['A']++;
      } else if (mp['C'] < m) {
        cout << "C";
        mp['C']++;
      } else if (mp['G'] < m) {
        cout << "G";
        mp['G']++;
      } else if (mp['T'] < m) {
        cout << "T";
        mp['T']++;
      }
    }
  }
  cout << endl;
  return 0;
}
