import java.util.Scanner;
public class Main {

	public static void main(String[] args) {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	}
} Main public static void main(String[] args) {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	} main {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double R = sc.nextInt(); R sc.nextInt() sc.nextInt sc System.out.print(2 * R * 3.14) System.out.print System.out System System.out 2 * R * 3.14 2 * R * 3.14 2 R 3.14 String[] args args public class Main {

	public static void main(String[] args) {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	}
} public class Main {

	public static void main(String[] args) {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	}
} Main
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {

		//入力の読み込み処理
		Scanner sc = new Scanner(System.in);
		double R = sc.nextInt();

		//計算結果の表示
		System.out.print(2 * R * 3.14);
	}
}