#include<bits/stdc++.h> using namespace std; int main() { int a,b,a0,b0,abcdefghijk; double c; cin>>a0>>b0; if(a0%2==0) a=a0+1; else a=a0; if(b0%2==0) b=b0+1; else b=b0; c=((b-a)*0.5+1)*(b+a)*0.5; abcdefghijk=(int)c; cout<<abcdefghijk; }