#include <bits/stdc++.h>
using namespace std;
int main(){
    int n;
	float a;
	cin>>n;
	a=(n*1.0/4)*(n*1.0/4);
	cout<<fixed<<setprecision(2)<<a;
	return 0;	
}
/**************************************************************
	Problem: 1420
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:14 ms
	Memory:2072 kb
****************************************************************/