#include<bits/stdc++.h>
using namespace std;
int main(){
    const double PI=3.14;
    double x,p;
    cin>>x;
    p=(x*x)/(4*PI);
    printf("%.2f",p);
} 
/**************************************************************
	Problem: 1337
	User: binzicheng1
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/