        
import java.util.*;import java.io.*;import java.math.*;import java.lang.*;




class Main
{

   
    public static void process()throws IOException
    {

                  int r = ni();
                  double pie=3.141592653589793238;
                  double d = 2.0*pie*r;
                  pn(d);
       

     


       

   


    }     

            
           
    




    static AnotherReader sc;
    static PrintWriter out;
    public static void main(String[]args)throws IOException
    {
        out = new PrintWriter(System.out);
        sc=new AnotherReader();
        boolean oj = true;

       // oj = System.getProperty("ONLINE_JUDGE") != null;
       // if(!oj) sc=new AnotherReader(100);

       long s = System.currentTimeMillis();
         int t=1;//test cases
         while(t-->0)
            process();
        out.flush();
        //if(!oj)
         // System.out.println(System.currentTimeMillis()-s+"ms");
        System.out.close();  
    }

    static void pn(Object o){out.println(o);}
    static void p(Object o){out.print(o);}
    static void pni(Object o){out.println(o);System.out.flush();}
    static int ni()throws IOException{return sc.nextInt();}
    static long nl()throws IOException{return sc.nextLong();}
    static double nd()throws IOException{return sc.nextDouble();}
    static String nln()throws IOException{return sc.nextLine();}
    static long gcd(long a, long b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int gcd(int a, int b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int bit(long n)throws IOException{return (n==0)?0:(1+bit(n&(n-1)));}
    static boolean multipleTC=false;



/////////////////////////////////////////////////////////////////////////////////////////////////////////

    static class AnotherReader
    {
        BufferedReader br; StringTokenizer st;
        AnotherReader()throws FileNotFoundException
        {
              br=new BufferedReader(new InputStreamReader(System.in));
        }
        AnotherReader(int a)throws FileNotFoundException
        {
              br = new BufferedReader(new FileReader("input.txt"));
        }
        String next()throws IOException
        {
              while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                }
                return st.nextToken(); 
        }
        int nextInt() throws IOException
        {
                return Integer.parseInt(next());
        }
        long nextLong() throws IOException
        {  
                return Long.parseLong(next());
        }
        double nextDouble()throws IOException 
        { 
               return Double.parseDouble(next()); 
        }
        String nextLine() throws IOException
        { 
               String str = ""; 
               try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } return str;
        }
    }
    
/////////////////////////////////////////////////////////////////////////////////////////////////////////////
}
    
    
    
     import java.util.*; util.* java import java.io.*; io.* java import java.math.*; math.* java import java.lang.*; lang.* java class Main
{

   
    public static void process()throws IOException
    {

                  int r = ni();
                  double pie=3.141592653589793238;
                  double d = 2.0*pie*r;
                  pn(d);
       

     


       

   


    }     

            
           
    




    static AnotherReader sc;
    static PrintWriter out;
    public static void main(String[]args)throws IOException
    {
        out = new PrintWriter(System.out);
        sc=new AnotherReader();
        boolean oj = true;

       // oj = System.getProperty("ONLINE_JUDGE") != null;
       // if(!oj) sc=new AnotherReader(100);

       long s = System.currentTimeMillis();
         int t=1;//test cases
         while(t-->0)
            process();
        out.flush();
        //if(!oj)
         // System.out.println(System.currentTimeMillis()-s+"ms");
        System.out.close();  
    }

    static void pn(Object o){out.println(o);}
    static void p(Object o){out.print(o);}
    static void pni(Object o){out.println(o);System.out.flush();}
    static int ni()throws IOException{return sc.nextInt();}
    static long nl()throws IOException{return sc.nextLong();}
    static double nd()throws IOException{return sc.nextDouble();}
    static String nln()throws IOException{return sc.nextLine();}
    static long gcd(long a, long b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int gcd(int a, int b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int bit(long n)throws IOException{return (n==0)?0:(1+bit(n&(n-1)));}
    static boolean multipleTC=false;



/////////////////////////////////////////////////////////////////////////////////////////////////////////

    static class AnotherReader
    {
        BufferedReader br; StringTokenizer st;
        AnotherReader()throws FileNotFoundException
        {
              br=new BufferedReader(new InputStreamReader(System.in));
        }
        AnotherReader(int a)throws FileNotFoundException
        {
              br = new BufferedReader(new FileReader("input.txt"));
        }
        String next()throws IOException
        {
              while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                }
                return st.nextToken(); 
        }
        int nextInt() throws IOException
        {
                return Integer.parseInt(next());
        }
        long nextLong() throws IOException
        {  
                return Long.parseLong(next());
        }
        double nextDouble()throws IOException 
        { 
               return Double.parseDouble(next()); 
        }
        String nextLine() throws IOException
        { 
               String str = ""; 
               try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } return str;
        }
    }
    
/////////////////////////////////////////////////////////////////////////////////////////////////////////////
} Main static AnotherReader sc; sc static PrintWriter out; out static boolean multipleTC=false; multipleTC false public static void process()throws IOException
    {

                  int r = ni();
                  double pie=3.141592653589793238;
                  double d = 2.0*pie*r;
                  pn(d);
       

     


       

   


    } process {

                  int r = ni();
                  double pie=3.141592653589793238;
                  double d = 2.0*pie*r;
                  pn(d);
       

     


       

   


    } int r = ni(); r ni() ni double pie=3.141592653589793238; pie 3.141592653589793238 double d = 2.0*pie*r; d 2.0*pie*r 2.0*pie*r 2.0 pie r pn(d) pn d public static void main(String[]args)throws IOException
    {
        out = new PrintWriter(System.out);
        sc=new AnotherReader();
        boolean oj = true;

       // oj = System.getProperty("ONLINE_JUDGE") != null;
       // if(!oj) sc=new AnotherReader(100);

       long s = System.currentTimeMillis();
         int t=1;//test cases
         while(t-->0)
            process();
        out.flush();
        //if(!oj)
         // System.out.println(System.currentTimeMillis()-s+"ms");
        System.out.close();  
    } main {
        out = new PrintWriter(System.out);
        sc=new AnotherReader();
        boolean oj = true;

       // oj = System.getProperty("ONLINE_JUDGE") != null;
       // if(!oj) sc=new AnotherReader(100);

       long s = System.currentTimeMillis();
         int t=1;//test cases
         while(t-->0)
            process();
        out.flush();
        //if(!oj)
         // System.out.println(System.currentTimeMillis()-s+"ms");
        System.out.close();  
    } out = new PrintWriter(System.out) out new PrintWriter(System.out) sc=new AnotherReader() sc new AnotherReader() boolean oj = true; oj true long s = System.currentTimeMillis(); s System.currentTimeMillis() System.currentTimeMillis System int t=1; t 1 while(t-->0)
            process(); t-->0 t-- t 0 process() process out.flush() out.flush out System.out.close() System.out.close System.out System System.out String[]args args static void pn(Object o){out.println(o);} pn {out.println(o);} out.println(o) out.println out o Object o o static void p(Object o){out.print(o);} p {out.print(o);} out.print(o) out.print out o Object o o static void pni(Object o){out.println(o);System.out.flush();} pni {out.println(o);System.out.flush();} out.println(o) out.println out o System.out.flush() System.out.flush System.out System System.out Object o o static int ni()throws IOException{return sc.nextInt();} ni {return sc.nextInt();} return sc.nextInt(); sc.nextInt() sc.nextInt sc static long nl()throws IOException{return sc.nextLong();} nl {return sc.nextLong();} return sc.nextLong(); sc.nextLong() sc.nextLong sc static double nd()throws IOException{return sc.nextDouble();} nd {return sc.nextDouble();} return sc.nextDouble(); sc.nextDouble() sc.nextDouble sc static String nln()throws IOException{return sc.nextLine();} nln {return sc.nextLine();} return sc.nextLine(); sc.nextLine() sc.nextLine sc static long gcd(long a, long b)throws IOException{return (b==0)?a:gcd(b,a%b);} gcd {return (b==0)?a:gcd(b,a%b);} return (b==0)?a:gcd(b,a%b); (b==0)?a:gcd(b,a%b) (b==0) b 0 a gcd(b,a%b) gcd b a%b a b long a a long b b static int gcd(int a, int b)throws IOException{return (b==0)?a:gcd(b,a%b);} gcd {return (b==0)?a:gcd(b,a%b);} return (b==0)?a:gcd(b,a%b); (b==0)?a:gcd(b,a%b) (b==0) b 0 a gcd(b,a%b) gcd b a%b a b int a a int b b static int bit(long n)throws IOException{return (n==0)?0:(1+bit(n&(n-1)));} bit {return (n==0)?0:(1+bit(n&(n-1)));} return (n==0)?0:(1+bit(n&(n-1))); (n==0)?0:(1+bit(n&(n-1))) (n==0) n 0 0 (1+bit(n&(n-1))) 1 bit(n&(n-1)) bit n&(n-1) n (n-1) n 1 long n n static class AnotherReader
    {
        BufferedReader br; StringTokenizer st;
        AnotherReader()throws FileNotFoundException
        {
              br=new BufferedReader(new InputStreamReader(System.in));
        }
        AnotherReader(int a)throws FileNotFoundException
        {
              br = new BufferedReader(new FileReader("input.txt"));
        }
        String next()throws IOException
        {
              while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                }
                return st.nextToken(); 
        }
        int nextInt() throws IOException
        {
                return Integer.parseInt(next());
        }
        long nextLong() throws IOException
        {  
                return Long.parseLong(next());
        }
        double nextDouble()throws IOException 
        { 
               return Double.parseDouble(next()); 
        }
        String nextLine() throws IOException
        { 
               String str = ""; 
               try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } return str;
        }
    } AnotherReader BufferedReader br; br StringTokenizer st; st AnotherReader()throws FileNotFoundException
        {
              br=new BufferedReader(new InputStreamReader(System.in));
        } AnotherReader {
              br=new BufferedReader(new InputStreamReader(System.in));
        } br=new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) AnotherReader(int a)throws FileNotFoundException
        {
              br = new BufferedReader(new FileReader("input.txt"));
        } AnotherReader {
              br = new BufferedReader(new FileReader("input.txt"));
        } br = new BufferedReader(new FileReader("input.txt")) br new BufferedReader(new FileReader("input.txt")) int a a String next()throws IOException
        {
              while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                }
                return st.nextToken(); 
        } next {
              while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                }
                return st.nextToken(); 
        } while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                } try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     } catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     } IOException  e {
                               e.printStackTrace(); 
                     } e.printStackTrace() e.printStackTrace e {
                               st = new StringTokenizer(br.readLine());
                     } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() throws IOException
        {
                return Integer.parseInt(next());
        } nextInt {
                return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() throws IOException
        {  
                return Long.parseLong(next());
        } nextLong {  
                return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble()throws IOException 
        { 
               return Double.parseDouble(next()); 
        } nextDouble { 
               return Double.parseDouble(next()); 
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() throws IOException
        { 
               String str = ""; 
               try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } return str;
        } nextLine { 
               String str = ""; 
               try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } return str;
        } String str = ""; str "" try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } catch (IOException e)
               {
                          e.printStackTrace();
               } IOException e {
                          e.printStackTrace();
               } e.printStackTrace() e.printStackTrace e {
                     str = br.readLine();
               } str = br.readLine() str br.readLine() br.readLine br return str; str
        
import java.util.*;import java.io.*;import java.math.*;import java.lang.*;




class Main
{

   
    public static void process()throws IOException
    {

                  int r = ni();
                  double pie=3.141592653589793238;
                  double d = 2.0*pie*r;
                  pn(d);
       

     


       

   


    }     

            
           
    




    static AnotherReader sc;
    static PrintWriter out;
    public static void main(String[]args)throws IOException
    {
        out = new PrintWriter(System.out);
        sc=new AnotherReader();
        boolean oj = true;

       // oj = System.getProperty("ONLINE_JUDGE") != null;
       // if(!oj) sc=new AnotherReader(100);

       long s = System.currentTimeMillis();
         int t=1;//test cases
         while(t-->0)
            process();
        out.flush();
        //if(!oj)
         // System.out.println(System.currentTimeMillis()-s+"ms");
        System.out.close();  
    }

    static void pn(Object o){out.println(o);}
    static void p(Object o){out.print(o);}
    static void pni(Object o){out.println(o);System.out.flush();}
    static int ni()throws IOException{return sc.nextInt();}
    static long nl()throws IOException{return sc.nextLong();}
    static double nd()throws IOException{return sc.nextDouble();}
    static String nln()throws IOException{return sc.nextLine();}
    static long gcd(long a, long b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int gcd(int a, int b)throws IOException{return (b==0)?a:gcd(b,a%b);}
    static int bit(long n)throws IOException{return (n==0)?0:(1+bit(n&(n-1)));}
    static boolean multipleTC=false;



/////////////////////////////////////////////////////////////////////////////////////////////////////////

    static class AnotherReader
    {
        BufferedReader br; StringTokenizer st;
        AnotherReader()throws FileNotFoundException
        {
              br=new BufferedReader(new InputStreamReader(System.in));
        }
        AnotherReader(int a)throws FileNotFoundException
        {
              br = new BufferedReader(new FileReader("input.txt"));
        }
        String next()throws IOException
        {
              while (st == null || !st.hasMoreElements()) 
                {
                    try
                     {
                               st = new StringTokenizer(br.readLine());
                     }
                    catch (IOException  e)
                    {
                               e.printStackTrace(); 
                     }
                }
                return st.nextToken(); 
        }
        int nextInt() throws IOException
        {
                return Integer.parseInt(next());
        }
        long nextLong() throws IOException
        {  
                return Long.parseLong(next());
        }
        double nextDouble()throws IOException 
        { 
               return Double.parseDouble(next()); 
        }
        String nextLine() throws IOException
        { 
               String str = ""; 
               try
               {
                     str = br.readLine();
               }
               catch (IOException e)
               {
                          e.printStackTrace();
               } return str;
        }
    }
    
/////////////////////////////////////////////////////////////////////////////////////////////////////////////
}
    
    
    
    