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