import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int r = sc.nextInt();

		System.out.println(Math.PI * 2 * r);
	}

} import java.util.ArrayList; ArrayList java.util import java.util.Collections; Collections java.util import java.util.List; List java.util import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int r = sc.nextInt();

		System.out.println(Math.PI * 2 * r);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int r = sc.nextInt();

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

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

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int r = sc.nextInt();

		System.out.println(Math.PI * 2 * r);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int r = sc.nextInt();

		System.out.println(Math.PI * 2 * r);
	}

} Main
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int r = sc.nextInt();

		System.out.println(Math.PI * 2 * r);
	}

}
