#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n, i;
  cin >> n;
  string s;
  cin >> s;
  map<char, int> m;
  char a[4] = {'A', 'C', 'G', 'T'};
  vector<pair<int, char>> v;
  if (n % 4 != 0)
    cout << "===";
  else {
    for (i = 0; i < s.length(); ++i) {
      if (s[i] != '?') m[s[i]]++;
    }
    for (i = 0; i < 4; ++i) {
      v.push_back(make_pair(m[a[i]], a[i]));
    }
    sort(v.begin(), v.end());
    for (i = 0; i < n; ++i) {
      if (s[i] == '?') {
        s[i] = v[0].second;
        v[0].first++;
        sort(v.begin(), v.end());
      }
    }
    for (i = 0; i < 3; ++i) {
      if (v[i].first != v[i + 1].first) break;
    }
    if (i == 3)
      cout << s;
    else
      cout << "===";
  }
  return 0;
}
