#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b;
	cin>>a>>b;
	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 a=a+1;
	for(int i=0;i<=b;i+=2)a+=i;
	cout<<a;
	return 0;
}