import java.util.*;
public class Solution {

	/**
	 * @param args the command line arguments
	 * @throws IOException
	 */
static Scanner s=new Scanner(System.in);
	public static void main(String[] args) throws IOException {
      {
		double r=s.nextDouble();
	System.out.println("the circumference = "+ 2*3.14*r);
	
		
		
	
	
	
		
	  }
}
	}