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

/**************************************************************
	Problem: 1420
	User: xuezihong1
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/