#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
const ll INF = 1e18;
const int MOD = 1000000007;


int main() {
    double a,b;
    cin >> a >> b;
    cout << setprecision(7) << (b-a)*(b-a)*(b-a) / 6 << endl;

    return 0;  
}