#include<stdio.h>
int main()
{
	int c;
	scanf("%d",&c);
	printf("%.2f",(c*1.0/4)*(c*1.0/4));
	return 0;
}
/**************************************************************
	Problem: 1420
	User: admin
	Language: C
	Result: Accepted
	Time:8 ms
	Memory:1144 kb
****************************************************************/