#include<bits/stdc++.h>
using namespace std;
int main(){ 
    int a;
    double h,z;
    cin>>a;
    h=a/4.0;
    z=h*h;
    printf("%.2f",z);
     
}
/**************************************************************
	Problem: 1420
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/