if (n==0) {
  System.out.println(1);
} else {
    if (n%2==0) {
      for (i=2;i<n+1;i+=2) {
        p=p*i;
      }
      System.out.println(p);
    } else {
      for (i=1;i<n+1;i+=2) {
        p=p*i;
      }
      System.out.println(p);
    }
}