#include <iostream>
#include <bits/stdc++.h>
using namespace std;
const long long INF = 1LL<<60;


int main(){
    double a, b;
    cin >> a >> b;
    
    double ans = (b-a) * (b-a) * (b-a) / 6;
    
    cout << fixed << setprecision(15);
    cout << ans << endl;
}