import java.util.*;

public class Main{
    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    }
} import java.util.*; util.* java public class Main{
    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    }
} Main public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    } main {
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double Pie = 3.141592; Pie 3.141592 System.out.println(2*(double)R*Pie) System.out.println System.out System System.out 2*(double)R*Pie 2*(double)R*Pie 2 (double)R Pie String[]args args public class Main{
    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    }
} public class Main{
    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    }
} Main
import java.util.*;

public class Main{
    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        int R = sc.nextInt();
        double Pie = 3.141592;
        System.out.println(2*(double)R*Pie);
    }
}