import java.util.*;

public class Main {
    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    }
} Main public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    } main {

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double d = Math.PI * sc.nextInt() * 2; d Math.PI * sc.nextInt() * 2 Math.PI * sc.nextInt() * 2 Math.PI Math Math.PI sc.nextInt() sc.nextInt sc 2 System.out.format("%f", d) System.out.format System.out System System.out "%f" d String[] args args public class Main {
    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    }
} public class Main {
    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args){

        Scanner sc = new Scanner(System.in);
        double d = Math.PI * sc.nextInt() * 2;
        System.out.format("%f", d);
    }
}