Circle_Square

#include<iostream>
#include<cmath>

using namespace std;

const double PI=acos(-1.0);

int main() {
    float n;
    cin >> n;
    double r = (PI/2 - atan(.5))*2;
    //cout << r << endl;
    double area = ((n*(n/2.0)) - 2*PI*(n/4.0)*(n/4.0))/8;
    //cout << n/4 << endl;
    double farea = (.5*(n/4.0)*(n/2.0))-(.5*(n/4.0)*(n/4.0)*(r-sin(r)))-area;
    cout << farea << endl;
    return 0;
}