/* package codechef; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Codechef
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner input = new Scanner(System.in);
		float n = input.nextFloat();
		 
		System.out.println(Math.PI * n *n);
	}
}
