import java.util.Scanner;

class Main{
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        int R = stdIn.nextInt();
        double pie = 3.141952;
        double L = 0.0;
        L = 2 * pie * (double)R;
        System.out.print(L);

    }
}  import java.util.Scanner; Scanner java.util class Main{
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        int R = stdIn.nextInt();
        double pie = 3.141952;
        double L = 0.0;
        L = 2 * pie * (double)R;
        System.out.print(L);

    }
} Main public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        int R = stdIn.nextInt();
        double pie = 3.141952;
        double L = 0.0;
        L = 2 * pie * (double)R;
        System.out.print(L);

    } main {
        Scanner stdIn = new Scanner(System.in);
        int R = stdIn.nextInt();
        double pie = 3.141952;
        double L = 0.0;
        L = 2 * pie * (double)R;
        System.out.print(L);

    } Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) int R = stdIn.nextInt(); R stdIn.nextInt() stdIn.nextInt stdIn double pie = 3.141952; pie 3.141952 double L = 0.0; L 0.0 L = 2 * pie * (double)R L 2 * pie * (double)R 2 * pie * (double)R 2 pie (double)R System.out.print(L) System.out.print System.out System System.out L String[] args args
import java.util.Scanner;

class Main{
    public static void main(String[] args){
        Scanner stdIn = new Scanner(System.in);
        int R = stdIn.nextInt();
        double pie = 3.141952;
        double L = 0.0;
        L = 2 * pie * (double)R;
        System.out.print(L);

    }
} 