#include<bits/stdc++.h>
using namespace std;

int main(){
    double a,b;
    cin>>a>>b;
    double ans;
    ans=(pow(a,3)-pow(b,3))/3-pow(a+b,2)*(a-b)/2+a*b*(a-b);
    printf("%f\n",ans);
    return 0;
}