
import java.util.Scanner;

public class Main {
    private static double pi =3.14;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
}


} import java.util.Scanner; Scanner java.util public class Main {
    private static double pi =3.14;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
}


} Main private static double pi =3.14; pi 3.14 public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
} main {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc double b = a*2*pi; b a*2*pi a*2*pi a 2 pi System.out.println(b) System.out.println System.out System System.out b String[] args args public class Main {
    private static double pi =3.14;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
}


} public class Main {
    private static double pi =3.14;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
}


} Main

import java.util.Scanner;

public class Main {
    private static double pi =3.14;
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        double b = a*2*pi;
        System.out.println(b);
        
    
}


}
