#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
    float m;
    cin>>n;
    m=(n/4.0)*(n/4.0);
	printf("%.2f",m);
}

/**************************************************************
	Problem: 1420
	User: shiruoxi
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/