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

int main(){
	double s,c,r,pi = 3.14;
	cin>>c;
	r = c / (2 * pi);
	s = pi * r * r;
	cout<<fixed<<setprecision(2)<<s<<endl;
	 
    return 0;
}

/**************************************************************
	Problem: 1337
	User: admin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/