#include<iostream>
using namespace std;
int main(){
    int n,m;
    cin >> m >> n;
    if(m%2==0)
    {
        m = m+1;
    }
    if(n%2==0)
    {
        n = n-1;
    }
    cout <<(n-m)*(n+m)/4+(n+m)/2;
    
}