import java.io.*;
import java.util.*;

public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    }
} import java.io.*; io.* java import java.util.*; util.* java public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    }
} Main public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    } main {
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double r=sc.nextInt(); r sc.nextInt() sc.nextInt sc System.out.println(2.0*Math.PI*r) System.out.println System.out System System.out 2.0*Math.PI*r 2.0*Math.PI*r 2.0 Math.PI Math Math.PI r String[] args args public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    }
} public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    }
} Main
import java.io.*;
import java.util.*;

public class Main{
    public static void main(String[] args)throws Exception{
        Scanner sc = new Scanner(System.in);
        double r=sc.nextInt();
        System.out.println(2.0*Math.PI*r);
    }
}