#include<cstdio>
using namespace std;
int main(){
	int c;
	scanf("%d",&c);
	float b=c/4.0;
	float s=b*b;
	printf("%.2f",s); 
	return 0;
}
/**************************************************************
	Problem: 1420
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:1144 kb
****************************************************************/