#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
using namespace std;
float a, r, p, Stron, Stg;
int main()
{
    freopen("area2.inp","r",stdin);
    freopen("area2.out","w",stdout);
    cout << setprecision(2) << fixed;
    cin >> a;
    r = sqrt(3)*a/3;
    Stron = r*r*3.14;
    p = 3*a/2;
    Stg = sqrt(p*(p-a)*(p-a)*(p-a));
    cout << Stron - Stg;
    return 0;
}

#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
int main() {
double a;
cin>>a;
double s=3.14*pow((a*pow(3,0.5)/3),2)-(a*a*pow(3,0.5))/4;
cout<<fixed<<setprecision(2)<<s<<endl;
return 0;
}