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