import java.util.*;

public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int R = sc.nextInt();
		System.out.printf("%.5f", Math.PI*2*R);
		sc.close();		
	}

} import java.util.*; util.* java public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int R = sc.nextInt();
		System.out.printf("%.5f", Math.PI*2*R);
		sc.close();		
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int R = sc.nextInt();
		System.out.printf("%.5f", Math.PI*2*R);
		sc.close();		
	} main {
		Scanner sc = new Scanner(System.in);
		int R = sc.nextInt();
		System.out.printf("%.5f", Math.PI*2*R);
		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.printf("%.5f", Math.PI*2*R) System.out.printf System.out System System.out "%.5f" Math.PI*2*R Math.PI*2*R Math.PI Math Math.PI 2 R 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.printf("%.5f", Math.PI*2*R);
		sc.close();		
	}

} public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int R = sc.nextInt();
		System.out.printf("%.5f", Math.PI*2*R);
		sc.close();		
	}

} Main
import java.util.*;

public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int R = sc.nextInt();
		System.out.printf("%.5f", Math.PI*2*R);
		sc.close();		
	}

}