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