import java.io.*;

public class Main {
    public static void main (String[] args) throws Exception {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    }
} import java.io.*; io.* java public class Main {
    public static void main (String[] args) throws Exception {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    }
} Main public static void main (String[] args) throws Exception {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    } main {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    } BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in)); reader new BufferedReader (new InputStreamReader (System.in)) int R = Integer.parseInt (reader.readLine()); R Integer.parseInt (reader.readLine()) Integer.parseInt Integer reader.readLine() reader.readLine reader System.out.println (2 * R * Math.PI) System.out.println System.out System System.out 2 * R * Math.PI 2 * R * Math.PI 2 R Math.PI Math Math.PI String[] args args public class Main {
    public static void main (String[] args) throws Exception {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    }
} public class Main {
    public static void main (String[] args) throws Exception {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    }
} Main
import java.io.*;

public class Main {
    public static void main (String[] args) throws Exception {
        BufferedReader reader =
            new BufferedReader (new InputStreamReader (System.in));
        int R = Integer.parseInt (reader.readLine());
        System.out.println (2 * R * Math.PI);
    }
}