#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: wangyichen2
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/