import java.util.*;

public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  }
} Main public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  } main {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) double r=sc.nextInt(); r sc.nextInt() sc.nextInt sc System.out.println(3.1416*r*2) System.out.println System.out System System.out 3.1416*r*2 3.1416*r*2 3.1416 r 2 String[] args args public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  }
} public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  }
} Main
import java.util.*;

public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    double r=sc.nextInt();
    System.out.println(3.1416*r*2);
  }
}
