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);
}
}
}
}