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