#include<bits/stdc++.h>
using namespace std;
int main(){
	const double PI=3.14;
	double x,p;
	cin>>x;
	p=(x*x)/(4*PI);
	printf("%.2f",p);
} 
/**************************************************************
	Problem: 1337
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/