import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  }
} Main public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  } main {
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan double a = 2*n*3.1415926535; a 2*n*3.1415926535 2*n*3.1415926535 2 n 3.1415926535 System.out.println(a) System.out.println System.out System System.out a String[] args args public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  }
} public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  }
} Main
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();
    double a = 2*n*3.1415926535;
    System.out.println(a);
  }
}
