import java.io.*;
import java.util.*;
import java.math.*;
import java.text.*;
public class Main {
public static void main(String args[])
{
String a;
double n,nn;
double pi=3.1415926535897932384626433832795;
Scanner cin=new Scanner(System.in);
while(true)
{
n=cin.nextDouble();
if(n==0)
break;
nn=(n/pi)*n/2;
DecimalFormat df=new DecimalFormat();
df.setMaximumFractionDigits(2);
df.setMinimumFractionDigits(2);
a=df.format(nn);
a=a.replace(",", "");
System.out.println(a);
}
}
}