import java.io.*;
import java.math.*;
import java.text.*;
import java.util.*;
import java.util.regex.*;

public class Solution {

    /*
     * Complete the pageCount function below.
     */
    static int pageCount(int n, int p) 
    {
        int reminder = (n%2);
        int papers =  (n/2);
        int counter = 0;
        if(papers>p)
        {
            for(int i = 1; i<=p; i=i+2)
            {
                counter++;
            }
        }
        else if(papers<p)
        {
            for(int i = n; i>=p; i=i-2)
            {
                counter++;
            }
        }
        if(reminder==1)
        {
            counter = counter -1;
        }
        return counter;
    }

    private static final Scanner scanner = new Scanner(System.in);

    public static void main(String[] args) throws IOException {
        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));

        int n = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])*");

        int p = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])*");

        int result = pageCount(n, p);

        bufferedWriter.write(String.valueOf(result));
        bufferedWriter.newLine();

        bufferedWriter.close();

        scanner.close();
    }
}