import java.util.Scanner;

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

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