백준 #26057번 Большой удой

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		int a = sc.nextInt();
		int b = sc.nextInt();
		System.out.println(b * 2 - a);
		sc.close();
	}
}