#include <bits/stdc++.h>
using namespace std;
double x;
double const P=3.14;
double r;
double s;
int main(){
    cin>>x;
    r=x/(2.0*P);
    s=P*r*r*1.0;
    printf("%.2f",s);
	return 0;
}

/**************************************************************
	Problem: 1337
	User: zengdongxin
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/