import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    }
} Main public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    } main {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    } Scanner cin = new Scanner(System.in); cin new Scanner(System.in) int val = cin.nextInt(); val cin.nextInt() cin.nextInt cin System.out.println(4*val*Math.acos(0)) System.out.println System.out System System.out 4*val*Math.acos(0) 4*val*Math.acos(0) 4 val Math.acos(0) Math.acos Math 0 String[] args args public class Main {

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    }
} public class Main {

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int val = cin.nextInt();
        System.out.println(4*val*Math.acos(0));
    }
}
