#include<bits/stdc++.h>
using namespace std;
int main(){
	int a;
	float b;
	cin>>a;
	b=(a/4.0)*(a/4.0);
	printf("%.2f",b);
}
/**************************************************************
	Problem: 1420
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/