#include<bits/stdc++.h>
using namespace std;
int main(){
	int i;
	cin>>i;
	printf("%.2f",(i/4.0)*(i/4.0));
	
}
/**************************************************************
	Problem: 1420
	User: baizhoudeyueguang
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/