public static void main(String[] args) {
        
        System.out.println(count(2));
        System.out.println(count(4));
        System.out.println(count(6));
    
    }

    private static Integer count(int n){
        if(n == 0){
            return 1;
        }
        Integer sum = 1;
        for(int i = n ;  i >=1 ;i--){
            sum *= i;
        }
        return sum;
    }