#include <iostream>
#include <iomanip>

using ldouble = long double;

void solve() {
    ldouble a, b;
    std::cin >> a >> b;

    auto d = b - a;
    std::cout << std::fixed << std::setprecision(10)
              << d * d * d / 6 << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}