import java.math.BigDecimal;
import java.util.*;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  }
}   import java.math.BigDecimal; BigDecimal java.math import java.util.*; util.* java public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double x = sc.nextDouble(); x sc.nextDouble() sc.nextDouble sc double pi = 3.14; pi 3.14 BigDecimal ans = new BigDecimal(2*x*pi); ans new BigDecimal(2*x*pi) 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);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  }
} Main
import java.math.BigDecimal;
import java.util.*;
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double x = sc.nextDouble();
    double pi = 3.14;
    BigDecimal ans = new BigDecimal(2*x*pi);
    System.out.println(ans);
  }
}  