import java.util.Scanner;
public class Main{


    public static void main(String[] args) {


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




    }

}

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


    public static void main(String[] args) {


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




    }

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


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




    } main {


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




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


    public static void main(String[] args) {


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




    }

} public class Main{


    public static void main(String[] args) {


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




    }

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


    public static void main(String[] args) {


        Scanner reader = new Scanner(System.in);

        int a = reader.nextInt();

            System.out.println(2*Math.PI*a);




    }

}


