
import java.util.*;
import java.io.*;

import static java.lang.Character.isUpperCase;

public class Main {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 }

    }







 import java.util.*; util.* java import java.io.*; io.* java import static java.lang.Character.isUpperCase; import static java.lang.Character.isUpperCase; import static java.lang.Character.isUpperCase; public class Main {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 }

    } Main public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 } main {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 } Scanner in = new Scanner(System.in); in new Scanner(System.in) int R = in.nextInt(); R in.nextInt() in.nextInt in System.out.println(2*3.14*R) System.out.println System.out System System.out 2*3.14*R 2*3.14*R 2 3.14 R String[] args args public class Main {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 }

    } public class Main {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 }

    } Main

import java.util.*;
import java.io.*;

import static java.lang.Character.isUpperCase;

public class Main {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int R = in.nextInt();

        System.out.println(2*3.14*R);
 }

    }








