#include<bits/stdc++.h>
using namespace std;
int main(){
    float x;
    cin>>x;
    printf("%.2f",(x/3.14/2)*(x/3.14/2)*3.14);
    return 0;
} 
/**************************************************************
	Problem: 1337
	User: panjinyan
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/