import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		double  pi = Math.PI;
		int n = 0;
		n = sc.nextInt();

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

			System.out.println((double)2*pi*n);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		double  pi = Math.PI;
		int n = 0;
		n = sc.nextInt();

			System.out.println((double)2*pi*n);
	} main {
		Scanner sc = new Scanner(System.in);
		double  pi = Math.PI;
		int n = 0;
		n = sc.nextInt();

			System.out.println((double)2*pi*n);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double  pi = Math.PI; pi Math.PI Math Math.PI int n = 0; n 0 n = sc.nextInt() n sc.nextInt() sc.nextInt sc System.out.println((double)2*pi*n) System.out.println System.out System System.out (double)2*pi*n (double)2*pi*n (double)2 pi n String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		double  pi = Math.PI;
		int n = 0;
		n = sc.nextInt();

			System.out.println((double)2*pi*n);
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		double  pi = Math.PI;
		int n = 0;
		n = sc.nextInt();

			System.out.println((double)2*pi*n);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		double  pi = Math.PI;
		int n = 0;
		n = sc.nextInt();

			System.out.println((double)2*pi*n);
	}
}