#include <bits/stdc++.h>
using namespace std;
int main() {
	float c,pi=3.14,r,s;
	scanf("%f",&c);
	r=c/pi/2;
	s=pi*r*r*1.0;
	printf("%.2f",s);
	return 0;
}
/**************************************************************
	Problem: 1337
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2076 kb
****************************************************************/