import java.util.Scanner;
import java.lang.Math;
class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double X = 3.1415926535;
        System.out.print(R*2*X);

        sc.close();
    }
} import java.util.Scanner; Scanner java.util import java.lang.Math; Math java.lang class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double X = 3.1415926535;
        System.out.print(R*2*X);

        sc.close();
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double X = 3.1415926535;
        System.out.print(R*2*X);

        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double X = 3.1415926535;
        System.out.print(R*2*X);

        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double X = 3.1415926535; X 3.1415926535 System.out.print(R*2*X) System.out.print System.out System System.out R*2*X R*2*X R 2 X sc.close() sc.close sc String[] args args
import java.util.Scanner;
import java.lang.Math;
class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double X = 3.1415926535;
        System.out.print(R*2*X);

        sc.close();
    }
}