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();

                        int sum=0;

                        for(int num=a;num<=b;num++){
                        	if(num%2==0){
                        		sum += num;
                        	}
                        }

                        System.out.println(sum);
                }

        }

}