import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan= new Scanner(System.in);
		int n=scan.nextInt();
		System.out.println((2*Math.PI*n));

	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner scan= new Scanner(System.in);
		int n=scan.nextInt();
		System.out.println((2*Math.PI*n));

	}

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

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

	} Scanner scan= new Scanner(System.in); scan new Scanner(System.in) int n=scan.nextInt(); n scan.nextInt() scan.nextInt scan System.out.println((2*Math.PI*n)) System.out.println System.out System System.out (2*Math.PI*n) 2*Math.PI*n 2 Math.PI Math Math.PI n String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scan= new Scanner(System.in);
		int n=scan.nextInt();
		System.out.println((2*Math.PI*n));

	}

} public class Main {

	public static void main(String[] args) {
		Scanner scan= new Scanner(System.in);
		int n=scan.nextInt();
		System.out.println((2*Math.PI*n));

	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan= new Scanner(System.in);
		int n=scan.nextInt();
		System.out.println((2*Math.PI*n));

	}

}
