import java.util.Scanner;
 
public class Main {
    public static void main(String[] args) {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    }
} Main public static void main(String[] args) {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    } main {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    } int R = 0; R 0 double sum = 0; sum 0 Scanner scan = new Scanner(System.in); scan new Scanner(System.in) R = scan.nextInt() R scan.nextInt() scan.nextInt scan sum = R * 2 * 3.141592 sum R * 2 * 3.141592 R * 2 * 3.141592 R 2 3.141592 System.out.println(sum) System.out.println System.out System System.out sum scan.close() scan.close scan String[] args args public class Main {
    public static void main(String[] args) {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    }
} public class Main {
    public static void main(String[] args) {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    }
} Main
import java.util.Scanner;
 
public class Main {
    public static void main(String[] args) {
        int R = 0;
        double sum = 0;
        Scanner scan = new Scanner(System.in);
        R = scan.nextInt();
        sum = R * 2 * 3.141592;
        System.out.println(sum);
        scan.close();
    }
}