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

int main() {
    double a,b,stht,sthcn,pi=3.14;
    cin >> a>>b;
    stht=a*a*pi/4;
    sthcn=a*b;
    //meothinhle
    cout<< fixed << setprecision(2) << sthcn-stht;
    return 0;
}

`@`$\color{#ff978c}{Mai}\color{#ff92f5} {Tuấn}\color{#b080ff}{Dũng}$

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

int main()
{
    double a,b;
    cin>>a>>b;
    cout<<fixed<<setprecision(2)<<a*b-3.14*(a/2)*(a/2);
    return 0;
}