#include<bits/stdc++.h>
using namespace std;
int main() {
	float x,p,b,s=0; 
	cin>>x;
	b=x/2/3.14;
	s=b*b*3.14;
	printf("%.2f",s);
	 
}

/**************************************************************
	Problem: 1337
	User: chenjunlin
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/