#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float s,a;
	cin>>n;
	a=n*1.00/4;
	s=a*a;
	printf("%.2f",s);
	return 0;
}

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