import java.util.*;
import java.lang.Math;
public class Main{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    }
} import java.util.*; util.* java import java.lang.Math; Math java.lang public class Main{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    }
} Main public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    } main {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) int r=sc.nextInt(); r sc.nextInt() sc.nextInt sc System.out.println(2.0 * Math.PI * (double)r) System.out.println System.out System System.out 2.0 * Math.PI * (double)r 2.0 * Math.PI * (double)r 2.0 Math.PI Math Math.PI (double)r sc.close() sc.close sc String[] args args public class Main{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    }
} public class Main{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    }
} Main
import java.util.*;
import java.lang.Math;
public class Main{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int r=sc.nextInt();
        System.out.println(2.0 * Math.PI * (double)r);
      sc.close();

    }
}
