import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    }
} Main public static void main(String[] args) {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    } main {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    } Long R; R Scanner sc = new Scanner(System.in); sc new Scanner(System.in) R = sc.nextLong() R sc.nextLong() sc.nextLong sc double Chu_vi =+R*2*Math.PI; Chu_vi +R*2*Math.PI +R*2*Math.PI +R R 2 Math.PI Math Math.PI System.out.println(Chu_vi) System.out.println System.out System System.out Chu_vi String[] args args public class Main {
    public static void main(String[] args) {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    }
} public class Main {
    public static void main(String[] args) {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Long R;
        Scanner sc = new Scanner(System.in);
        R = sc.nextLong();
        double Chu_vi =+R*2*Math.PI;
        //String.format("%.25g%n", Chu_vi);
        System.out.println(Chu_vi);

    }
}
