import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    }
} Main public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    } main {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    } Scanner tan = new Scanner(System.in); tan new Scanner(System.in) int r=tan.nextInt(); r tan.nextInt() tan.nextInt tan double p=2*Math.PI*r; p 2*Math.PI*r 2*Math.PI*r 2 Math.PI Math Math.PI r System.out.printf("%.20f\n",p) System.out.printf System.out System System.out "%.20f\n" p String[] args args public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        int r=tan.nextInt();
        double p=2*Math.PI*r;
        System.out.printf("%.20f\n",p);
    }
}
