#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int flag = 0, x;
  int a = 0, t = 0, c = 0, g = 0;
  if (n % 4) {
    flag = 1;
    char muku[300];
    scanf("%s", muku);
    cout << "===";
  } else {
    x = n / 4;
    char muku[300], ans[300];
    scanf("%s", muku);
    for (int i = 0; i < n; i++) {
      if (muku[i] == 'A') {
        a++;
      } else if (muku[i] == 'T') {
        t++;
      } else if (muku[i] == 'C') {
        c++;
      } else if (muku[i] == 'G') {
        g++;
      } else if (muku[i] == '?') {
      }
    }
    if (a > x || c > x || g > x || t > x) {
      cout << "===";
    } else {
      for (int i = 0; i < n; i++) {
        if (muku[i] != '?') {
          ans[i] = muku[i];
          cout << ans[i];
        } else {
          if (x - a > 0) {
            ans[i] = 'A';
            a++;
          } else if (x - t > 0) {
            ans[i] = 'T';
            t++;
          } else if (x - c > 0) {
            ans[i] = 'C';
            c++;
          } else if (x - g > 0) {
            ans[i] = 'G';
            g++;
          }
          cout << ans[i];
        }
      }
    }
  }
  return 0;
}
