import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    }
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    } main {
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int r = sc.nextInt(); r sc.nextInt() sc.nextInt sc double res = Math.round(2 * 3.1415*r*100)/100.0; res Math.round(2 * 3.1415*r*100)/100.0 Math.round(2 * 3.1415*r*100) Math.round Math 2 * 3.1415*r*100 r 2 * 3.1415*r*100 2 3.1415 r 100 100.0 System.out.println(res) System.out.println System.out System System.out res String[] args args public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    }
} public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double res = Math.round(2 * 3.1415*r*100)/100.0;
        System.out.println(res);
    }
}
