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