import java.util.*;

public class Main {
public static void main(String args[]) {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
}
} import java.util.*; util.* java public class Main {
public static void main(String args[]) {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
}
} Main public static void main(String args[]) {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
} main {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
} Scanner sc=new Scanner(System.in); sc new Scanner(System.in) double h=sc.nextDouble(); h sc.nextDouble() sc.nextDouble sc double r=h*2*3.14; r h*2*3.14 h*2*3.14 h 2 3.14 System.out.println(r) System.out.println System.out System System.out r String args[] args public class Main {
public static void main(String args[]) {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
}
} public class Main {
public static void main(String args[]) {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
}
} Main
import java.util.*;

public class Main {
public static void main(String args[]) {
	Scanner sc=new Scanner(System.in);
	double h=sc.nextDouble();
	double r=h*2*3.14;
	
    System.out.println(r);
}
}
