#include<bits/stdc++.h>
using namespace std;
int n;
int main(){
	cin>>n;
  printf(" %.2f",n*1.0/4*(n*1.0/4));

	return 0;
}

/**************************************************************
	Problem: 1420
	User: wangyousi
	Language: C++
	Result: Presentation Error
****************************************************************/