import java.math.*;
import java.util.*;
public class Main
{
    public static void main(String[] args)
    {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    }
} import java.math.*; math.* java import java.util.*; util.* java public class Main
{
    public static void main(String[] args)
    {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    }
} Main public static void main(String[] args)
    {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    } main {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    } BigDecimal pi=new BigDecimal("3.14159265359"); pi new BigDecimal("3.14159265359") Scanner sc = new Scanner(System.in); sc new Scanner(System.in) BigDecimal m = sc.nextBigDecimal(); m sc.nextBigDecimal() sc.nextBigDecimal sc System.out.println(m.multiply(pi).multiply(new BigDecimal(2))) System.out.println System.out System System.out m.multiply(pi).multiply(new BigDecimal(2)) m.multiply(pi).multiply m.multiply(pi) m.multiply m pi new BigDecimal(2) String[] args args public class Main
{
    public static void main(String[] args)
    {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    }
} public class Main
{
    public static void main(String[] args)
    {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    }
} Main
import java.math.*;
import java.util.*;
public class Main
{
    public static void main(String[] args)
    {
    	BigDecimal pi=new BigDecimal("3.14159265359");
    	Scanner sc = new Scanner(System.in);
    	BigDecimal m = sc.nextBigDecimal();
    	System.out.println(m.multiply(pi).multiply(new BigDecimal(2)));
    	
    }
}