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

public class Main{

	public static void main(String[] args) {
		Main cd = new Main();
        System.out.println(cd.calculate());
	}

    private final String ERROR_INPUT_INT = "入力値は実数ではありません。";

    private String input() throws IOException{
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    }


    public Integer inputInt() { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    }

	public double calculate() {
		return 2*this.inputInt()*Math.PI;
	}

} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io public class Main{

	public static void main(String[] args) {
		Main cd = new Main();
        System.out.println(cd.calculate());
	}

    private final String ERROR_INPUT_INT = "入力値は実数ではありません。";

    private String input() throws IOException{
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    }


    public Integer inputInt() { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    }

	public double calculate() {
		return 2*this.inputInt()*Math.PI;
	}

} Main private final String ERROR_INPUT_INT = "入力値は実数ではありません。"; ERROR_INPUT_INT "入力値は実数ではありません。" public static void main(String[] args) {
		Main cd = new Main();
        System.out.println(cd.calculate());
	} main {
		Main cd = new Main();
        System.out.println(cd.calculate());
	} Main cd = new Main(); cd new Main() System.out.println(cd.calculate()) System.out.println System.out System System.out cd.calculate() cd.calculate cd String[] args args private String input() throws IOException{
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    } input {
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    } String line; line BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); reader new BufferedReader(new InputStreamReader(System.in)) line = reader.readLine() line reader.readLine() reader.readLine reader return line; line public Integer inputInt() { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    } inputInt { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    } try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        } catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        } Exception s {
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        } System.out.println(ERROR_INPUT_INT) System.out.println System.out System System.out ERROR_INPUT_INT return this.inputInt(); this.inputInt() this.inputInt this {
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        } String value = this.input(); value this.input() this.input this Integer n = Integer.parseInt(value); n Integer.parseInt(value) Integer.parseInt Integer value return n; n public double calculate() {
		return 2*this.inputInt()*Math.PI;
	} calculate {
		return 2*this.inputInt()*Math.PI;
	} return 2*this.inputInt()*Math.PI; 2*this.inputInt()*Math.PI 2*this.inputInt()*Math.PI 2 this.inputInt() this.inputInt this Math.PI Math Math.PI public class Main{

	public static void main(String[] args) {
		Main cd = new Main();
        System.out.println(cd.calculate());
	}

    private final String ERROR_INPUT_INT = "入力値は実数ではありません。";

    private String input() throws IOException{
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    }


    public Integer inputInt() { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    }

	public double calculate() {
		return 2*this.inputInt()*Math.PI;
	}

} public class Main{

	public static void main(String[] args) {
		Main cd = new Main();
        System.out.println(cd.calculate());
	}

    private final String ERROR_INPUT_INT = "入力値は実数ではありません。";

    private String input() throws IOException{
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    }


    public Integer inputInt() { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    }

	public double calculate() {
		return 2*this.inputInt()*Math.PI;
	}

} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main{

	public static void main(String[] args) {
		Main cd = new Main();
        System.out.println(cd.calculate());
	}

    private final String ERROR_INPUT_INT = "入力値は実数ではありません。";

    private String input() throws IOException{
        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        line = reader.readLine();
        return line;
    }


    public Integer inputInt() { //double型の数値を入力できるメソッド
        try{
            String value = this.input();
            Integer n = Integer.parseInt(value);
            return n;
        }
        catch (Exception s){
            System.out.println(ERROR_INPUT_INT);
            return this.inputInt();
        }
    }

	public double calculate() {
		return 2*this.inputInt()*Math.PI;
	}

}