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>b){
int temp = a;
a=b;
b=temp;
}//swap
int sum=0;
for(int num=a;num<=b;num++){
if(num%2==0){
sum += num;
}
}
System.out.println(sum);
}
}
}