

import java.util.Scanner;

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

		double p = 2*data*Math.PI;

		System.out.println(p);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		long data = scan.nextLong();

		double p = 2*data*Math.PI;

		System.out.println(p);
	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		long data = scan.nextLong();

		double p = 2*data*Math.PI;

		System.out.println(p);
	} main {
		Scanner scan = new Scanner(System.in);
		long data = scan.nextLong();

		double p = 2*data*Math.PI;

		System.out.println(p);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) long data = scan.nextLong(); data scan.nextLong() scan.nextLong scan double p = 2*data*Math.PI; p 2*data*Math.PI 2*data*Math.PI 2 data Math.PI Math Math.PI System.out.println(p) System.out.println System.out System System.out p String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		long data = scan.nextLong();

		double p = 2*data*Math.PI;

		System.out.println(p);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		long data = scan.nextLong();

		double p = 2*data*Math.PI;

		System.out.println(p);
	}
} Main


import java.util.Scanner;

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

		double p = 2*data*Math.PI;

		System.out.println(p);
	}
}