ABCD == DABC * 2

/*we need to multiply our first digit by 2
until we get a 2 with no carry over.

When we have a multiplication that exceeds 9,
we add the remainder to the digit and add 1 to the next
multiplication.*/

public class Solution {
    public static void main(String[] args){
        int b=2;
        boolean remainder=false;
        StringBuilder number = new StringBuilder("2");
        do{
                if (!remainder) {
                    b *= 2;
                } else {
                    b = b * 2 + 1;
                }
                if (b < 10) {
                    number.append(b);
                    remainder = false;
                } else {
                    number.append(b%10);
                    b %= 10;
                    remainder = true;
                }
            if(b/2==1 && b%2==0 && !remainder){break;}
        }while(true);
        String new_number = number.reverse().toString();
        new_number=new_number.substring(1,number.length());
        long result = Long.parseLong(new_number);
        System.out.println(result);
    }
}