#include <iostream>
#include <cmath>
using namespace std;
int main()
{
double s = 0.0;
double a = 100.0;
float b = 0.001f;
cout << "Enter a, b\n";
cin >> a >> b;
s = (pow(a - b, 3) - pow(a, 3)) / (pow(b, 3) + 3 * pow(a * b, 2) - 3 * pow(a, 2) * b);
cout << s << endl;
system("pause");
}