import java.util.Scanner;

class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = scan.nextInt();
    double n = r*2*3.14;
    System.out.println(n);
  }
} import java.util.Scanner; Scanner java.util class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = scan.nextInt();
    double n = r*2*3.14;
    System.out.println(n);
  }
} Main public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = scan.nextInt();
    double n = r*2*3.14;
    System.out.println(n);
  } main {
    Scanner scan = new Scanner(System.in);
    int r = scan.nextInt();
    double n = r*2*3.14;
    System.out.println(n);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int r = scan.nextInt(); r scan.nextInt() scan.nextInt scan double n = r*2*3.14; n r*2*3.14 r*2*3.14 r 2 3.14 System.out.println(n) System.out.println System.out System System.out n String[] args args
import java.util.Scanner;

class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int r = scan.nextInt();
    double n = r*2*3.14;
    System.out.println(n);
  }
}
