import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long A = Integer.parseInt(sc.next());
        long B = Integer.parseInt(sc.next());

        long cnt = 0;
        if (A > B) {
            for (long i = A + 1; i <= 2000000000; i++) {
                cnt++;
            }
        } else {
            cnt = B - A -1;
        }

        System.out.println(cnt);
    }
}