import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		long A = scan.nextLong();
		long B = scan.nextLong();
		scan.close();
		long ans = 0;
		long max = 2000000000;
		if(A < B) {
			ans = B - 2;
		}else {
			ans = max - B - 1;
		}
		System.out.println(ans);
	}
}