#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float d,p=0;
	scanf("%d",&n);
	d=n/4.0;
	p=d*d;
	printf("%.2f",p);
} 
/**************************************************************
	Problem: 1420
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2076 kb
****************************************************************/