import java.util.Scanner;
import java.lang.Math;
class Main {
    public static void main(String args[]) {
      Scanner scan = new Scanner(System.in);
      int r = scan.nextInt();
      System.out.printf("%.20f",2*Math.PI*r);
    }
} import java.util.Scanner; Scanner java.util import java.lang.Math; Math java.lang class Main {
    public static void main(String args[]) {
      Scanner scan = new Scanner(System.in);
      int r = scan.nextInt();
      System.out.printf("%.20f",2*Math.PI*r);
    }
} Main public static void main(String args[]) {
      Scanner scan = new Scanner(System.in);
      int r = scan.nextInt();
      System.out.printf("%.20f",2*Math.PI*r);
    } main {
      Scanner scan = new Scanner(System.in);
      int r = scan.nextInt();
      System.out.printf("%.20f",2*Math.PI*r);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int r = scan.nextInt(); r scan.nextInt() scan.nextInt scan System.out.printf("%.20f",2*Math.PI*r) System.out.printf System.out System System.out "%.20f" 2*Math.PI*r 2*Math.PI*r 2 Math.PI Math Math.PI r String args[] args
import java.util.Scanner;
import java.lang.Math;
class Main {
    public static void main(String args[]) {
      Scanner scan = new Scanner(System.in);
      int r = scan.nextInt();
      System.out.printf("%.20f",2*Math.PI*r);
    }
}
