import java.util.*;

public class Practicer {

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

		while(cin.hasNext()){
			int a = cin.nextInt();
			int b = cin.nextInt();

			if( (a%2!=0) && (b%2!=0) )
			{
				System.out.println((b-a)/2);
			}
			else{
				System.out.println((b-a)/2+1);
			}
		}

	}

}