public static void main(String a[]){
        List<Integer> numbers = new ArrayList<Integer>();
        for(int i=1;i<30;i++){
            numbers.add(i);
        }
        //add duplicate number into the list
        numbers.add(5);
        FindDuplicateNum fdn = new FindDuplicateNum();
        System.out.println("Duplicate Number: "+fdn.findDuplicateNumber(numbers));
    }