import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  }
} import java.util.*; util.* java public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  } main {
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double r = sc.nextLong(); r sc.nextLong() sc.nextLong sc double result = 2 * r * 3.14; result 2 * r * 3.14 2 * r * 3.14 2 r 3.14 System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  }
} public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  }
} Main
import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    
    // 半径の長さ
    double r = sc.nextLong();

    // 円周の長さ
    double result = 2 * r * 3.14;
    System.out.println(result);
  }
}