/* 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. */
public class Main
{
	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 * 2 *n);
	}
} import java.util.*; util.* java import java.lang.*; lang.* java import java.io.*; io.* java public class Main
{
	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 * 2 *n);
	}
} Main 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 * 2 *n);
	} main {
		Scanner input = new Scanner(System.in);
		float n = input.nextFloat();
		 
		System.out.println(Math.PI * 2 *n);
	} Scanner input = new Scanner(System.in); input new Scanner(System.in) float n = input.nextFloat(); n input.nextFloat() input.nextFloat input System.out.println(Math.PI * 2 *n) System.out.println System.out System System.out Math.PI * 2 *n Math.PI * 2 *n Math.PI Math Math.PI 2 n String[] args args public class Main
{
	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 * 2 *n);
	}
} public class Main
{
	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 * 2 *n);
	}
} Main
/* 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. */
public class Main
{
	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 * 2 *n);
	}
}
