import java.util.*;

class Main{
  public static void main(String[] args){
    
    Scanner scanner = new Scanner(System.in);
    int R = scanner.nextInt();
    double X = 2*3.14159265*R;
    System.out.println(X);
    
  }
} import java.util.*; util.* java class Main{
  public static void main(String[] args){
    
    Scanner scanner = new Scanner(System.in);
    int R = scanner.nextInt();
    double X = 2*3.14159265*R;
    System.out.println(X);
    
  }
} Main public static void main(String[] args){
    
    Scanner scanner = new Scanner(System.in);
    int R = scanner.nextInt();
    double X = 2*3.14159265*R;
    System.out.println(X);
    
  } main {
    
    Scanner scanner = new Scanner(System.in);
    int R = scanner.nextInt();
    double X = 2*3.14159265*R;
    System.out.println(X);
    
  } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int R = scanner.nextInt(); R scanner.nextInt() scanner.nextInt scanner double X = 2*3.14159265*R; X 2*3.14159265*R 2*3.14159265*R 2 3.14159265 R System.out.println(X) System.out.println System.out System System.out X String[] args args
import java.util.*;

class Main{
  public static void main(String[] args){
    
    Scanner scanner = new Scanner(System.in);
    int R = scanner.nextInt();
    double X = 2*3.14159265*R;
    System.out.println(X);
    
  }
}
