import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    }
} Main public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    } main {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    } Scanner s1 = new Scanner(System.in); s1 new Scanner(System.in) double result = 2 * Math.PI * s1.nextInt(); result 2 * Math.PI * s1.nextInt() 2 * Math.PI * s1.nextInt() 2 Math.PI Math Math.PI s1.nextInt() s1.nextInt s1 System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {

    public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    }
} public class Main {

    public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        double result = 2 * Math.PI * s1.nextInt();
        System.out.println(result);
    }
}
