import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    } main {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    } Scanner input = new Scanner(System.in); input new Scanner(System.in) double R = input.nextInt(); R input.nextInt() input.nextInt input double ans = 2*R*Math.PI; ans 2*R*Math.PI 2*R*Math.PI 2 R Math.PI Math Math.PI System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    }
} Main
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double R = input.nextInt();
        double ans = 2*R*Math.PI;
        System.out.println(ans);
    }
}