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 = B + 1 ; i < A; i++) cnt++;
        } else {
            for (long i = 1; i < B; i++) {
                cnt++;
            }
        }

        System.out.println(cnt);
    }
}