#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1000000007;
const long long N = 1e9 + 5;
const long long Hash = 31;
const double pi = 3.141592653;
const double E = 2.718281828;
void solve() {
  int n;
  string s;
  cin >> n >> s;
  if (n % 4) {
    cout << "===";
    return;
  }
  int num[5] = {0};
  for (int i = 0; i < n; i++) {
    if (s[i] == 'A')
      num[0]++;
    else if (s[i] == 'C')
      num[1]++;
    else if (s[i] == 'G')
      num[2]++;
    else if (s[i] == 'T')
      num[3]++;
    else
      num[4]++;
  }
  for (int i = 0; i < 4; i++) {
    num[i] = (n / 4) - num[i];
    if (num[i] < 0) {
      cout << "===";
      return;
    }
  }
  int tag = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] == '?') {
      while (num[tag] == 0) tag++;
      num[tag]--;
      if (tag == 0)
        cout << 'A';
      else if (tag == 1)
        cout << 'C';
      else if (tag == 2)
        cout << 'G';
      else
        cout << 'T';
    } else
      cout << s[i];
  }
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int t = 1;
  while (t--) solve();
  return 0;
}
