#include<bits/stdc++.h>
using namespace std;
int main(){
	int n=0;
	float a;
    cin>>n;
    a=n/4.0;
    printf("%.2f",a*a);
}
 
/**************************************************************
	Problem: 1420
	User: lvrenxiang
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/