#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	 cin>>n;
	printf("%.2f",(n/4.0)*(n/4.0));
	return 0;
}
/**************************************************************
	Problem: 1420
	User: zhangailin
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/