import java.util.Scanner;

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

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