import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    }
} Main public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    } main {
        Scanner scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int radius = scan.nextInt(); radius scan.nextInt() scan.nextInt scan double result = 2 * 3.14 * radius; result 2 * 3.14 * radius 2 * 3.14 * radius 2 3.14 radius 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 scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int radius = scan.nextInt();
        double result = 2 * 3.14 * radius;

        System.out.println(result);
    }
}