#include<bits/stdc++.h>
using namespace std;
int n;
int main(){
cin>>n;
float p=n/4.00;
float s=p*p;
printf("%.2f",s);

	return 0;
}

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