import java.util.Scanner;

class Main {

    public static void main(String[] args) {
        Scanner stdIn=new Scanner(System.in);
        
        double x;
        double y=Math.PI;
        do{
            
            
           x=stdIn.nextInt(); 
        }while(x<=1&&x>=100);
        
        System.out.println(x*2*y);
        
    }

} import java.util.Scanner; Scanner java.util class Main {

    public static void main(String[] args) {
        Scanner stdIn=new Scanner(System.in);
        
        double x;
        double y=Math.PI;
        do{
            
            
           x=stdIn.nextInt(); 
        }while(x<=1&&x>=100);
        
        System.out.println(x*2*y);
        
    }

} Main public static void main(String[] args) {
        Scanner stdIn=new Scanner(System.in);
        
        double x;
        double y=Math.PI;
        do{
            
            
           x=stdIn.nextInt(); 
        }while(x<=1&&x>=100);
        
        System.out.println(x*2*y);
        
    } main {
        Scanner stdIn=new Scanner(System.in);
        
        double x;
        double y=Math.PI;
        do{
            
            
           x=stdIn.nextInt(); 
        }while(x<=1&&x>=100);
        
        System.out.println(x*2*y);
        
    } Scanner stdIn=new Scanner(System.in); stdIn new Scanner(System.in) double x; x double y=Math.PI; y Math.PI Math Math.PI do{
            
            
           x=stdIn.nextInt(); 
        }while(x<=1&&x>=100); x<=1&&x>=100 x<=1 x 1 x>=100 x 100 {
            
            
           x=stdIn.nextInt(); 
        } x=stdIn.nextInt() x stdIn.nextInt() stdIn.nextInt stdIn System.out.println(x*2*y) System.out.println System.out System System.out x*2*y x*2*y x 2 y String[] args args
import java.util.Scanner;

class Main {

    public static void main(String[] args) {
        Scanner stdIn=new Scanner(System.in);
        
        double x;
        double y=Math.PI;
        do{
            
            
           x=stdIn.nextInt(); 
        }while(x<=1&&x>=100);
        
        System.out.println(x*2*y);
        
    }

}