    import java.util.Scanner;
    import java.lang.Math;
    import java.math.BigDecimal;
     
    class Main{
     
        public static void main(String[] args){
     
            Scanner scanner = new Scanner(System.in);
            int r = scanner.nextInt();
            scanner.close();
            BigDecimal bd1 = new BigDecimal(2.0 * r);
            BigDecimal bd2 = new BigDecimal(Math.PI);
            BigDecimal result = bd1.multiply(bd2);
            System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP));
     
        }
     
    } import java.util.Scanner; Scanner java.util import java.lang.Math; Math java.lang import java.math.BigDecimal; BigDecimal java.math class Main{
     
        public static void main(String[] args){
     
            Scanner scanner = new Scanner(System.in);
            int r = scanner.nextInt();
            scanner.close();
            BigDecimal bd1 = new BigDecimal(2.0 * r);
            BigDecimal bd2 = new BigDecimal(Math.PI);
            BigDecimal result = bd1.multiply(bd2);
            System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP));
     
        }
     
    } Main public static void main(String[] args){
     
            Scanner scanner = new Scanner(System.in);
            int r = scanner.nextInt();
            scanner.close();
            BigDecimal bd1 = new BigDecimal(2.0 * r);
            BigDecimal bd2 = new BigDecimal(Math.PI);
            BigDecimal result = bd1.multiply(bd2);
            System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP));
     
        } main {
     
            Scanner scanner = new Scanner(System.in);
            int r = scanner.nextInt();
            scanner.close();
            BigDecimal bd1 = new BigDecimal(2.0 * r);
            BigDecimal bd2 = new BigDecimal(Math.PI);
            BigDecimal result = bd1.multiply(bd2);
            System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP));
     
        } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int r = scanner.nextInt(); r scanner.nextInt() scanner.nextInt scanner scanner.close() scanner.close scanner BigDecimal bd1 = new BigDecimal(2.0 * r); bd1 new BigDecimal(2.0 * r) BigDecimal bd2 = new BigDecimal(Math.PI); bd2 new BigDecimal(Math.PI) BigDecimal result = bd1.multiply(bd2); result bd1.multiply(bd2) bd1.multiply bd1 bd2 System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP)) System.out.println System.out System System.out result.setScale(2, BigDecimal.ROUND_HALF_UP) result.setScale result 2 BigDecimal.ROUND_HALF_UP BigDecimal BigDecimal.ROUND_HALF_UP String[] args args
    import java.util.Scanner;
    import java.lang.Math;
    import java.math.BigDecimal;
     
    class Main{
     
        public static void main(String[] args){
     
            Scanner scanner = new Scanner(System.in);
            int r = scanner.nextInt();
            scanner.close();
            BigDecimal bd1 = new BigDecimal(2.0 * r);
            BigDecimal bd2 = new BigDecimal(Math.PI);
            BigDecimal result = bd1.multiply(bd2);
            System.out.println(result.setScale(2, BigDecimal.ROUND_HALF_UP));
     
        }
     
    }