import java.util.*;

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

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

        scan.close();
        return;
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

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

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

        scan.close();
        return;
    } main {
        Scanner scan = new Scanner(System.in);

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

        scan.close();
        return;
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) double r = scan.nextInt(); r scan.nextInt() scan.nextInt scan System.out.println(2 * Math.PI * r) System.out.println System.out System System.out 2 * Math.PI * r 2 * Math.PI * r 2 Math.PI Math Math.PI r scan.close() scan.close scan return; String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

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

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

        scan.close();
        return;
    }
} Main
import java.util.*;

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

        double r = scan.nextInt();
        System.out.println(2 * Math.PI * r);

        scan.close();
        return;
    }
}