import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) System.out.println(Math.PI*Integer.parseInt(sc.next())*2) System.out.println System.out System System.out Math.PI*Integer.parseInt(sc.next())*2 Math.PI*Integer.parseInt(sc.next())*2 Math.PI Math Math.PI Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc 2 sc.close() sc.close sc String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);     
        System.out.println(Math.PI*Integer.parseInt(sc.next())*2);
        sc.close();
    }
}