import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    } main {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double radius = sc.nextDouble(); radius sc.nextDouble() sc.nextDouble sc System.out.println(2*Math.PI*radius) System.out.println System.out System System.out 2*Math.PI*radius 2*Math.PI*radius 2 Math.PI Math Math.PI radius String[] args args public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    }
} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius = sc.nextDouble();
        System.out.println(2*Math.PI*radius);
    }
}