#include<bits/stdc++.h>
using namespace std;
int main(){
    float a;
    cin>>a;
    printf("%.2f",(a/3.14/2)*(a/3.14/2)*3.14);
    return 0;
}
/**************************************************************
	Problem: 1337
	User: linyuhang
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/