import java.util.Scanner;

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

        int n = scan.nextInt();
        int k = scan.nextInt();

        if(n<3){
            System.out.println(0);
            return;
        }

        System.out.println(Math.max(k - 1, n - k) - 2);
    }
}

your programm works only because of weak tests.
for example: 3 1
your answer is 0, but the correct one is 1.
1 _ _
1 _ 3
1 2 3 -> there is 1 person from both sides and the distance to number 2 is equal, so in the worst case the person will hit vasya.

Edited by author 13.01.2016 01:14

Edited by author 13.01.2016 01:14

n is even