#include <bits/stdc++.h>
using namespace std;
//天下无双，个数平方
/*
这也钛坚氮了
*/
int enumk(int n,int m){
    if(m%2==1&&n%2==1)return (m-n)/2+1;
    if((m%2==1&&n%2==0)||(m%2==0&&n%2==1))return (m-n-1)/2+1;
    return (m-n-2)/2+1;
}
int main(){
    int x,y,n1,n2;
    cin>>x>>y;
    if(x==0)x=1;
    n1=enumk(1,y)*enumk(1,y);
    n2=enumk(1,x-1)*enumk(1,x-1);
    cout<<n1-n2;
}