백준 #3046번 R2

import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		
		Scanner sc = new Scanner(System.in);
		
		int r1 = sc.nextInt();
		int s = sc.nextInt();
		int r2 = 2 * s - r1;
		
		System.out.println(r2);
		sc.close();
	}
}