import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in); 
      int a = input.nextInt();
      System.out.println(a*6.28);
    }
} import java.util.Scanner; Scanner java.util class Main {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in); 
      int a = input.nextInt();
      System.out.println(a*6.28);
    }
} Main public static void main(String[] args) {
		Scanner input = new Scanner(System.in); 
      int a = input.nextInt();
      System.out.println(a*6.28);
    } main {
		Scanner input = new Scanner(System.in); 
      int a = input.nextInt();
      System.out.println(a*6.28);
    } Scanner input = new Scanner(System.in); input new Scanner(System.in) int a = input.nextInt(); a input.nextInt() input.nextInt input System.out.println(a*6.28) System.out.println System.out System System.out a*6.28 a 6.28 String[] args args
import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in); 
      int a = input.nextInt();
      System.out.println(a*6.28);
    }
}