import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    } main {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) System.out.println(scanner.nextDouble() * 2.0 * Math.PI) System.out.println System.out System System.out scanner.nextDouble() * 2.0 * Math.PI scanner.nextDouble() * 2.0 * Math.PI scanner.nextDouble() scanner.nextDouble scanner 2.0 Math.PI Math Math.PI String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println(scanner.nextDouble() * 2.0 * Math.PI);
    }
}
