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