import java.io.*;
import java.util.*;
public class Main
{
  public static void main(String args[])throws IOException
  {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  }
} import java.io.*; io.* java import java.util.*; util.* java public class Main
{
  public static void main(String args[])throws IOException
  {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  }
} Main public static void main(String args[])throws IOException
  {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  } main {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  } InputStreamReader read = new InputStreamReader(System.in); read new InputStreamReader(System.in) BufferedReader in = new BufferedReader(read); in new BufferedReader(read) double r=Double.parseDouble(in.readLine()); r Double.parseDouble(in.readLine()) Double.parseDouble Double in.readLine() in.readLine in double circum=(double)(2*(Math.PI)*r); circum (double)(2*(Math.PI)*r) 2*(Math.PI)*r 2 (Math.PI) Math Math.PI r System.out.println(circum) System.out.println System.out System System.out circum String args[] args public class Main
{
  public static void main(String args[])throws IOException
  {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  }
} public class Main
{
  public static void main(String args[])throws IOException
  {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  }
} Main
import java.io.*;
import java.util.*;
public class Main
{
  public static void main(String args[])throws IOException
  {
    InputStreamReader read = new InputStreamReader(System.in);
    BufferedReader in = new BufferedReader(read);
    double r=Double.parseDouble(in.readLine());
    double circum=(double)(2*(Math.PI)*r);
    System.out.println(circum);
  }
}