import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	}

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

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	}

} Main public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	} main {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	} Scanner scn = new Scanner(System.in); scn new Scanner(System.in) double R = scn.nextDouble(); R scn.nextDouble() scn.nextDouble scn scn.close() scn.close scn double ans = 2*R*3.1415926535; ans 2*R*3.1415926535 2*R*3.1415926535 2 R 3.1415926535 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	}

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

	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		double R = scn.nextDouble();
		scn.close();
		double ans = 2*R*3.1415926535;
		System.out.println(ans);
	}

}
