import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final long max = 2000000000l;
		final long min = 1;
		
		final long A = sc.nextLong();
		final long B = sc.nextLong();
		
		System.out.println(A < B ? (B - min - 1) : (max - B - 1));
	}

}