#include<stdio.h>
int main(){
int a,b,i,sum=0,temp;
while(scanf("%d%d",&a,&b)!=EOF){
if(a>b){
temp=a;
a=b;
b=temp;
}
if(a%2==1)
a+=1;
for(i=a;i<=b;i+=2){
sum+=i;
}
printf("%d\n",sum);
sum=0;
}
}