#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
int x, y;
cin >> x >> y;
if (x > y) swap(x, y); // 交换 x, y
int sum = 0;
for (int i = x + 1; i < y; i ++ )
{
if (i % 2) sum += i;
}
cout << sum << endl;
return 0;
}