#include <bits/stdc++.h>
using namespace std;

int main(){
	int n;
	cin>>n;
	cout<<fixed<<setprecision(2)<<n/4.0*n/4.0<<endl;
}
/**************************************************************
	Problem: 1420
	User: admin
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/