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