#include <bits/stdc++.h>
using namespace std;
int n, a = 0, c = 0, g = 0, t = 0, ques = 0, m = 0;
char f[400];
int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) cin >> f[i];
  if (n % 4 != 0) {
    cout << "===";
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (f[i] == 'A')
      a++;
    else if (f[i] == 'C')
      c++;
    else if (f[i] == 'G')
      g++;
    else if (f[i] == 'T')
      t++;
    else
      ques++;
  }
  m = n / 4;
  if (a > m || c > m || t > m || g > m) {
    cout << "===";
    return 0;
  }
  for (int i = 0; i < n; i++)
    if (f[i] == '?') {
      if (a < m) {
        f[i] = 'A';
        a++;
      } else if (c < m) {
        f[i] = 'C';
        c++;
      } else if (t < m) {
        f[i] = 'T';
        t++;
      } else if (g < m) {
        f[i] = 'G';
        g++;
      }
    }
  for (int i = 0; i < n; i++) cout << f[i];
}
