#include<iostream>
using namespace std;
int main(){
	int a,b;
	cin>>a>>b;
	int sum=0;
	if(a%2==1&&b%2==1){
		while(a!=b+2){
			sum+=a;
			a+=2;
		}
	}else if(a%2==0&&b%2==1){
		a++;
		while(a!=b+2){
			sum+=a;
			a+=2;
		}
	}else if(a%2==1&&b%2==0){
		b++;
		while(a!=b){
			sum+=a;
			a+=2;
		}
	}else{
		a++;

		while(a!=b+1){
			sum+=a;
			a+=2;
		}
	}cout<<sum;
}