import java.util.*;
import java.io.*;
public class Main{
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main{
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    }
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    } main {
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) PrintWriter ou = new PrintWriter(System.out); ou new PrintWriter(System.out) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc ou.print(Math.PI * 2.0 * n + "\n") ou.print ou Math.PI * 2.0 * n + "\n" Math.PI * 2.0 * n Math.PI * 2.0 * n Math.PI Math Math.PI 2.0 n "\n" ou.flush() ou.flush ou String[] args args public class Main{
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    }
} public class Main{
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    }
} Main
import java.util.*;
import java.io.*;
public class Main{
    public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		ou.print(Math.PI * 2.0 * n + "\n");
		ou.flush();
    }
}