#include<bits/stdc++.h>
using namespace std;
int main(){
	float s,a;
	cin>>a;
	s=(a/4)*(a/4);
	printf("%.2lf",s);
}

/**************************************************************
	Problem: 1420
	User: huxuanchen
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/