import java.util.*;

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

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