
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    }

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

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    }

} Main public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    } main {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int r = Integer.parseInt(scan.next()); r Integer.parseInt(scan.next()) Integer.parseInt Integer scan.next() scan.next scan scan.close() scan.close scan System.out.println(2*r*3.1415926535) System.out.println System.out System System.out 2*r*3.1415926535 2*r*3.1415926535 2 r 3.1415926535 String[] args args public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    }

} public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    }

} Main

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int r = Integer.parseInt(scan.next());
        scan.close();

        System.out.println(2*r*3.1415926535);
    }

}