#include<bits/stdc++.h>
using namespace std;
int main(){
	float a,n;
	cin>>n;
	a=n/4*(n/4);
	printf("%.2f",a);
	return 0; 
} 
/**************************************************************
	Problem: 1420
	User: tonghuatao
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/