#include<bits/stdc++.h>
using namespace std;
int main(){
    float s,a;
    cin>>a;
    s=(a/4)*(a/4);
    printf("%.2lf",s);
}
/**************************************************************
	Problem: 1420
	User: linyuhang
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/