include<iostream>

include<cmath>

using namespace std; int main() { long long a,b; cin>>a>>b; a+=abs(a)%2; b-=abs(b)%2; a-=2; long long e=b/2; long long d=a/2; long long u=e+1; long long r=e*u; long long t=d+1; long long o=d*t; cout<<r-o; return 0; }