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

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