import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

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

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

	}
} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

	} main {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) double R = scanner.nextDouble(); R scanner.nextDouble() scanner.nextDouble scanner double answer = 2 * R * Math.PI; answer 2 * R * Math.PI 2 * R * Math.PI 2 R Math.PI Math Math.PI System.out.println(answer) System.out.println System.out System System.out answer scanner.close() scanner.close scanner String[] args args public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

	}
} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner scanner = new Scanner(System.in);

		double R = scanner.nextDouble();

		double answer = 2 * R * Math.PI;

		System.out.println(answer);

		scanner.close();

	}
}