

import java.util.Scanner;

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

		int r = sc.nextInt();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

	}
} 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();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

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

		int r = sc.nextInt();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

	} main {
		Scanner sc = new Scanner(System.in);

		int r = sc.nextInt();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc double R = r * 2 * 3.14159; R r * 2 * 3.14159 r * 2 * 3.14159 r 2 3.14159 System.out.println(R) System.out.println System.out System System.out R sc.close() sc.close sc String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int r = sc.nextInt();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

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

		int r = sc.nextInt();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

	}
} Main


import java.util.Scanner;

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

		int r = sc.nextInt();
		double R = r * 2 * 3.14159;

		System.out.println(R);

		sc.close();

	}
}
