#include <bits/stdc++.h>
using namespace std;
int main() {
	float a,k,m;
	cin>>a;;
	k=a/2/3.14;
	m=3.14*k*k;
	printf("%.2f",m);
}
/**************************************************************
	Problem: 1337
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/