#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	double s=n/4.0;
    printf("%.2f",s*s);
	return 0;
}

/**************************************************************
	Problem: 1420
	User: duyahan
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/