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

/**************************************************************
	Problem: 1420
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/