#include <bits/stdc++.h>
using namespace std;
vector<int> v;
int main() {
  int n, a = 0, g = 0, c = 0, t = 0;
  cin >> n;
  string s;
  cin >> s;
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A')
      a++;
    else if (s[i] == 'G')
      g++;
    else if (s[i] == 'C')
      c++;
    else if (s[i] == 'T')
      t++;
    else
      v.push_back(i);
  }
  if (n % 4 != 0) {
    cout << "===" << endl;
    return 0;
  }
  int b = n / 4;
  if (a > b || g > b || c > b || t > b) {
    cout << "===" << endl;
    return 0;
  }
  for (int i = 0; i < v.size(); i++) {
    if (a < b) {
      s[v[i]] = 'A';
      a++;
    } else if (g < b) {
      s[v[i]] = 'G';
      g++;
    } else if (c < b) {
      s[v[i]] = 'C';
      c++;
    } else if (t < b) {
      s[v[i]] = 'T';
      t++;
    }
  }
  if (a == b && g == b && c == b && t == b)
    cout << s;
  else
    cout << "===" << endl;
  return 0;
}
