import java.util.Scanner;
public class Main{
    public static void main(String[]args){
        Scanner reader=new Scanner(System.in);
        double a=reader.nextDouble();
        double b=reader.nextDouble();
        System.out.println((int)(2.0*b-a));
    }
    //设第三项为c
}//b-a=c-b  
//b-a+b=c 
//c=2b-a