#include<bits/stdc++.h>
using namespace std;
int main(){

	float a,d,r,s;
	cin>>a;
	d=a/3.14;
	r=d/2;
	s=r*r*3.14;
	printf("%.2f",s);


	return 0;
}

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