#include <bits/stdc++.h>
using namespace std;
int main()
{
int a, b;
int sum = 0;
cin >> a >> b;
if(b < a)
{ int t = a;
a = b;
b = t;
}
for(int i = a + 1; i < b; i++)
{
if(i % 2 == 1 || i % 2 == -1)
{
sum = sum + i;
}
}
cout << sum << endl;
return 0;
}