import java.util.Scanner;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
    
        double circumference;
        double PI = 3.14159265;
        circumference = 2 * PI * R;
        System.out.println(circumference);
    }
} import java.util.Scanner; Scanner java.util class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
    
        double circumference;
        double PI = 3.14159265;
        circumference = 2 * PI * R;
        System.out.println(circumference);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
    
        double circumference;
        double PI = 3.14159265;
        circumference = 2 * PI * R;
        System.out.println(circumference);
    } main {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
    
        double circumference;
        double PI = 3.14159265;
        circumference = 2 * PI * R;
        System.out.println(circumference);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double circumference; circumference double PI = 3.14159265; PI 3.14159265 circumference = 2 * PI * R circumference 2 * PI * R 2 * PI * R 2 PI R System.out.println(circumference) System.out.println System.out System System.out circumference String[] args args
import java.util.Scanner;
class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
    
        double circumference;
        double PI = 3.14159265;
        circumference = 2 * PI * R;
        System.out.println(circumference);
    }
}