#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;
}

#include <bits/stdc++.h>
#define int long long
using namespace std;
signed main(){
	double a,b;
	cin>>a>>b;
	double rec=a*b;
	double areaCircle=(a/2)*(a/2)*3.14;//a/2 = ban kinh
	cout<<setprecision(2)<<fixed<<rec-areaCircle;//Dien tich hinh tron = r^2*3.14
}