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

/**************************************************************
	Problem: 1420
	User: zhengzihao3
	Language: C++
	Result: Wrong Answer
****************************************************************/