注意：末项为a

import java.util.Scanner;

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

        int res = 0;
        if (a % 2 == 0) {
            res = (a - n) / -2 + 1;
        }else {
            res = (a - 1) / 2 + 1;
        }
        System.out.println(res);
    }
}