import java.util.*;
public class java{
public static void main(String[] args){
int t,sum=0;
Scanner sc = new Scanner(System.in);
while(sc.hasNext()){
int x = sc.nextInt();
int y = sc.nextInt();
if(x>y){
t=x;
x=y;
y=t;
}
for(int i=x;i<=y;i++){
if(i%2==0){
sum+=i;
}
}
System.out.print(sum);
}
}
}