import java.util.Scanner;

public class Main {

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

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

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

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

public class Main {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		int R = sc.nextInt();
	System.out.println(2*R*3.14);
	sc.close();
  }
}