#include<bits/stdc++.h>
using namespace std;
int main(){
	int m,n,sum=0;
	cin>>m>>n;
	if(m%2==1){
		for(int i=m;i<=n;i+=2){
			sum+=i;
		}
	}
	else if(m%2==0){
		for(int i=m+1;i<=n;i+=2){
			sum+=i;
		}
	}
	cout<<sum;
	return 0;
}