import java.util.*;
public class Main {

    public static void main(String[] args) {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    }
} import java.util.*; util.* java public class Main {

    public static void main(String[] args) {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    }
} Main public static void main(String[] args) {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    } main {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    } Scanner  yomi = new Scanner(System.in); yomi new Scanner(System.in) double n = yomi.nextDouble(); n yomi.nextDouble() yomi.nextDouble yomi System.out.println(n*2*3.1415) System.out.println System.out System System.out n*2*3.1415 n*2*3.1415 n 2 3.1415 String[] args args public class Main {

    public static void main(String[] args) {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    }
} public class Main {

    public static void main(String[] args) {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    }
} Main
import java.util.*;
public class Main {

    public static void main(String[] args) {
        Scanner  yomi = new Scanner(System.in);
        double n = yomi.nextDouble();
        System.out.println(n*2*3.1415);

    }
}