public class Main {
    public static void main(String[] args) {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    }

    public static  String readLine(int maxLen){
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    }
} public class Main {
    public static void main(String[] args) {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    }

    public static  String readLine(int maxLen){
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    }
} Main public static void main(String[] args) {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    } main {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    } int value = Integer.parseInt(readLine(255)); value Integer.parseInt(readLine(255)) Integer.parseInt Integer readLine(255) readLine 255 System.out.printf("%f",(2*Math.PI*value)) System.out.printf System.out System System.out "%f" (2*Math.PI*value) 2*Math.PI*value 2 Math.PI Math Math.PI value String[] args args public static  String readLine(int maxLen){
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    } readLine {
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    } int[] holder = new int[maxLen]; holder new int[maxLen] maxLen int counter =0 counter 0 reader =1; reader 1 try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        } catch(Exception ex){
            return (null);
        } Exception ex {
            return (null);
        } return (null); (null) {
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        } while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            } counter < maxLen counter maxLen {
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            } reader = System.in.read() reader System.in.read() System.in.read System.in System System.in if(reader <0 || (reader =='\n'))break; reader <0 || (reader =='\n') reader <0 reader 0 (reader =='\n') reader '\n' break; holder[counter++] = reader holder[counter++] holder counter++ counter reader if(counter ==0 && reader <0)return (null); counter ==0 && reader <0 counter ==0 counter 0 reader <0 reader 0 return (null); (null) return new String(holder,0,counter); new String(holder,0,counter) int maxLen maxLen public class Main {
    public static void main(String[] args) {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    }

    public static  String readLine(int maxLen){
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    }
} public class Main {
    public static void main(String[] args) {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    }

    public static  String readLine(int maxLen){
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    }
} Main
public class Main {
    public static void main(String[] args) {
        int value = Integer.parseInt(readLine(255));
        System.out.printf("%f",(2*Math.PI*value));
    }

    public static  String readLine(int maxLen){
        int[] holder = new int[maxLen];
        int counter =0, reader =1;

        try{
            while(counter < maxLen){
                reader = System.in.read();
                if(reader <0 || (reader =='\n'))break;
                holder[counter++] = reader;
            }
        }catch(Exception ex){
            return (null);
        }

        if(counter ==0 && reader <0)return (null);
        return new String(holder,0,counter);
    }
}
