#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	printf("%.2f",n*1.0/4*(n*1.0/4));
	return 0;
}

/**************************************************************
	Problem: 1420
	User: panjinyan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/