import java.util.*;
 
public class Main{
  public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	}
} import java.util.*; util.* java public class Main{
  public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	} main {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double R = sc.nextDouble(); R sc.nextDouble() sc.nextDouble sc double x = Math.PI; x Math.PI Math Math.PI double num = 0; num 0 num =R * x * 2 num R * x * 2 R * x * 2 R x 2 System.out.println(num) System.out.println System.out System System.out num String[] args args public class Main{
  public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	}
} public class Main{
  public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	}
} Main
import java.util.*;
 
public class Main{
  public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R = sc.nextDouble();
		double x = Math.PI;
		double num = 0;
		num =R * x * 2;
		System.out.println(num);
	}
}