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