#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float s;
    cin>>n;
    s=n/4.0;
    cout<<fixed<<setprecision(2)<<s*s;
	return 0;
}

/**************************************************************
	Problem: 1420
	User: hongguangxi
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/