#include<stdio.h>

int main() {
	int a,b;
	int sum=0;
	scanf("%d%d",&a,&b);
	a=a+(a%2);
	b=b-(b%2);
	for(int i=a;i<=b;i+=2){
			sum+=i;
	}
	printf("%d",sum);
	return 0;
}