#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#define rep(i, a, n) for(int i = a; i < n; i++)
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main()
{
    double a, b;
    cin >> a >> b;
    printf("%.7f\n",  -pow(a-b, 3)/6);
    return 0;
}