#include<bits/stdc++.h>
using namespace std;
int main(){ 
	int a;
	double h,z;
	cin>>a;
	h=a/4.0;
	z=h*h;
	printf("%.2f",z);
	
}


/**************************************************************
	Problem: 1420
	User: zhuangsongyu
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/