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