#include <bits/stdc++.h>

using namespace std;

using ll = long double;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll a, b;
    cin >> a >> b;
    ll ans = b - a;
    ans = ans * ans * ans / 6;
    cout << fixed << setprecision(15) << ans << endl;
    return 0;
}