#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float m,M;
	cin>>n;
	m=n/4.0;
	M=m*m;
	printf("%.2f",M);
}
/**************************************************************
	Problem: 1420
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/