import java.util.*;

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

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