#include<bits/stdc++.h>
using namespace std;
int main(){
	float a,b;
	cin>>a;
	b=a/6.28*a/6.28*3.14;
	printf("%.2f",b);
	return 0;
}

/**************************************************************
	Problem: 1337
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/