#include<bits/stdc++.h>
using namespace std;
int n;
double b,s;
int main(){
	cin>>n;
	b=n/4.0;
	s=b*b;
	cout<<fixed<<setprecision(2)<<s;
	return 0;
}

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