import java.io.*;
import java.util.*;
import java.lang.Math;
public class Main{
	public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    }
} import java.io.*; io.* java import java.util.*; util.* java import java.lang.Math; Math java.lang public class Main{
	public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    }
} Main public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    } main {
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc System.out.println(+Math.PI*2*r) System.out.println System.out System System.out +Math.PI*2*r +Math.PI*2*r +Math.PI Math.PI Math Math.PI 2 r String args[] args public class Main{
	public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    }
} public class Main{
	public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    }
} Main
import java.io.*;
import java.util.*;
import java.lang.Math;
public class Main{
	public static void main(String args[]){
    	Scanner sc = new Scanner(System.in);
      int r = sc.nextInt();
      System.out.println(+Math.PI*2*r);
    }
}