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

	}

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

	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double R;
		double circumference;
		R = sc.nextDouble();
		
		circumference = 2*R*(Math.PI);
		
		System.out.println(circumference);

	} main {
		Scanner sc = new Scanner(System.in);
		double R;
		double circumference;
		R = sc.nextDouble();
		
		circumference = 2*R*(Math.PI);
		
		System.out.println(circumference);

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

	}

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

	}

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

	}

}