import java.util.Scanner;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  }
} import java.util.Scanner; Scanner java.util public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  } main {
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int c = sc.nextInt(); c sc.nextInt() sc.nextInt sc double d = c*2*3.14159; d c*2*3.14159 c*2*3.14159 c 2 3.14159 System.out.println(d) System.out.println System.out System System.out d String[] args args public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  }
} Main
import java.util.Scanner;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int c = sc.nextInt();
    double d = c*2*3.14159;
    System.out.println(d);
  }
}