import java.util.*;
import java.io.*;
public class Main
{
  public static void main(String args[])throws Exception
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  }
} import java.util.*; util.* java import java.io.*; io.* java public class Main
{
  public static void main(String args[])throws Exception
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  }
} Main public static void main(String args[])throws Exception
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  } main {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  } BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) PrintWriter pw=new PrintWriter(System.out); pw new PrintWriter(System.out) int r=Integer.parseInt(br.readLine()); r Integer.parseInt(br.readLine()) Integer.parseInt Integer br.readLine() br.readLine br pw.println(Math.PI*r*2) pw.println pw Math.PI*r*2 Math.PI*r*2 Math.PI Math Math.PI r 2 pw.flush() pw.flush pw pw.close() pw.close pw String args[] args public class Main
{
  public static void main(String args[])throws Exception
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  }
} public class Main
{
  public static void main(String args[])throws Exception
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  }
} Main
import java.util.*;
import java.io.*;
public class Main
{
  public static void main(String args[])throws Exception
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    PrintWriter pw=new PrintWriter(System.out);
    int r=Integer.parseInt(br.readLine());
    pw.println(Math.PI*r*2);
    pw.flush();
    pw.close();
  }
}