import java.util.Scanner;
public class Main {
public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();}} import java.util.Scanner; Scanner java.util public class Main {
public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();}} Main public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();} main {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int n = scanner.nextInt(); n scanner.nextInt() scanner.nextInt scanner double p = 3.1415926535897932384626433832795; p 3.1415926535897932384626433832795 System.out.println(2*n*p) System.out.println System.out System System.out 2*n*p 2*n*p 2 n p scanner.close() scanner.close scanner String[] args args public class Main {
public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();}} public class Main {
public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();}} Main
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
	Scanner scanner = new Scanner(System.in);
	int n = scanner.nextInt();
  	double p = 3.1415926535897932384626433832795;
  	System.out.println(2*n*p);
	scanner.close();}}