import java.util.*;

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

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

