#include<bits/stdc++.h>
using namespace std;
int main()
{
	long long int a,b,k;
	cin>>a>>b;
	k=a;
	if(a%2==0&&b%2==0){
		a=a+1;
		b=b-1;}
	else if(a%2==0&&b%2!=0)b=b-1;
	else if(a%2!=0&&b%2!=0)a=a,b=b;
	else a=a+1;//判断奇偶
	for(long long int i=a;i<=b;i+=2)a+=i;
	cout<<a-k;
	return 0;
}