import java.util.*;
import java.util.Collections;
import java.util.stream.Collectors;
 
public class Main {
 
  public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  }
} import java.util.*; util.* java import java.util.Collections; Collections java.util import java.util.stream.Collectors; Collectors java.util.stream public class Main {
 
  public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  }
} Main public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  } main {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  } Scanner s = new Scanner(System.in); s new Scanner(System.in) int num = s.nextInt(); num s.nextInt() s.nextInt s Double r = (double) num; r (double) num System.out.println(2*3.14*r) System.out.println System.out System System.out 2*3.14*r 2*3.14*r 2 3.14 r String[] args args public class Main {
 
  public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  }
} public class Main {
 
  public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  }
} Main
import java.util.*;
import java.util.Collections;
import java.util.stream.Collectors;
 
public class Main {
 
  public static void main(String[] args) {

	Scanner s = new Scanner(System.in);
		int num = s.nextInt();
		Double r = (double) num;
	System.out.println(2*3.14*r);
  }
}