import java.util.Scanner;

public class Main { 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    }
} import java.util.Scanner; Scanner java.util public class Main { 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    } main {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) long a = scanner.nextLong(); a scanner.nextLong() scanner.nextLong scanner System.out.println(2*a*3.14) System.out.println System.out System System.out 2*a*3.14 2*a*3.14 2 a 3.14 String[] args args public class Main { 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    }
} public class Main { 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    }
} Main
import java.util.Scanner;

public class Main { 
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = scanner.nextLong();
        System.out.println(2*a*3.14);


    }
}