

import java.io.BufferedReader;
import java.io.InputStreamReader;


public class Main {

    public static void main(String[] args) {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    }
}
     import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main {

    public static void main(String[] args) {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    }
} Main public static void main(String[] args) {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    } main {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    } try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        } catch (Exception e){
            e.printStackTrace();
        } Exception e {
            e.printStackTrace();
        } e.printStackTrace() e.printStackTrace e {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        } InputStreamReader is = new InputStreamReader(System.in); is new InputStreamReader(System.in) BufferedReader br = new BufferedReader(is); br new BufferedReader(is) int i = Integer.parseInt(br.readLine()); i Integer.parseInt(br.readLine()) Integer.parseInt Integer br.readLine() br.readLine br double c =Math.PI*2*i; c Math.PI*2*i Math.PI*2*i Math.PI Math Math.PI 2 i System.out.println(c) System.out.println System.out System System.out c String[] args args public class Main {

    public static void main(String[] args) {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    }
} public class Main {

    public static void main(String[] args) {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    }
} Main


import java.io.BufferedReader;
import java.io.InputStreamReader;


public class Main {

    public static void main(String[] args) {
        
        try {
            InputStreamReader is = new InputStreamReader(System.in);
            BufferedReader br = new BufferedReader(is);
            int i = Integer.parseInt(br.readLine());
            double c =Math.PI*2*i;
            System.out.println(c);
        }catch (Exception e){
            e.printStackTrace();
        }
        
    }
}
    
