#include <iostream>
#include <string>
#include <vector>
#include <numeric>

using namespace std;
int main() 
{
	int a, b;
	cin >> a;
	cin >> b;

	cout << (b - a) * (4 * a * b - (a + b) * (a + b)) / -6.0 << endl;

	return 0;
}