import java.util.Scanner;
import java.util.*;
public class Main {
    public static void main(String args[]){
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    }
} import java.util.Scanner; Scanner java.util import java.util.*; util.* java public class Main {
    public static void main(String args[]){
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    }
} Main public static void main(String args[]){
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    } main {
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    } int radius; radius double circumference; circumference Scanner sc = new Scanner(System.in); sc new Scanner(System.in) radius = sc.nextInt() radius sc.nextInt() sc.nextInt sc circumference = Math.PI*2*radius circumference Math.PI*2*radius Math.PI*2*radius Math.PI Math Math.PI 2 radius System.out.println(circumference) System.out.println System.out System System.out circumference String args[] args public class Main {
    public static void main(String args[]){
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    }
} public class Main {
    public static void main(String args[]){
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    }
} Main
import java.util.Scanner;
import java.util.*;
public class Main {
    public static void main(String args[]){
        int radius;
        double circumference;
        Scanner sc = new Scanner(System.in);

        radius = sc.nextInt();
        circumference = Math.PI*2*radius;
        System.out.println(circumference);
    }
}