import java.util.*;
public class Main {// Main
    public static void main(String[] args){
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    }
} import java.util.*; util.* java public class Main {// Main
    public static void main(String[] args){
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    }
} Main public static void main(String[] args){
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    } main {
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    } Scanner sc=new Scanner (System.in); sc new Scanner (System.in) double r=sc.nextDouble(); r sc.nextDouble() sc.nextDouble sc double circum=2*Math.PI*r; circum 2*Math.PI*r 2*Math.PI*r 2 Math.PI Math Math.PI r System.out.println(String.format("%.20f", circum)) System.out.println System.out System System.out String.format("%.20f", circum) String.format String "%.20f" circum String[] args args public class Main {// Main
    public static void main(String[] args){
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    }
} public class Main {// Main
    public static void main(String[] args){
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    }
} Main
import java.util.*;
public class Main {// Main
    public static void main(String[] args){
        	Scanner sc=new Scanner (System.in);
		
		double r=sc.nextDouble();
		double circum=2*Math.PI*r;
		System.out.println(String.format("%.20f", circum));
    }
}