import java.util.Scanner;
public class Main {
	  public static void main(String args[]){
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
}
	  } import java.util.Scanner; Scanner java.util public class Main {
	  public static void main(String args[]){
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
}
	  } Main public static void main(String args[]){
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
} main {
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) double a=scanner.nextDouble(); a scanner.nextDouble() scanner.nextDouble scanner double c=a*2*3.14; c a*2*3.14 a*2*3.14 a 2 3.14 System.out.println(c) System.out.println System.out System System.out c String args[] args public class Main {
	  public static void main(String args[]){
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
}
	  } public class Main {
	  public static void main(String args[]){
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
}
	  } Main
import java.util.Scanner;
public class Main {
	  public static void main(String args[]){
	 Scanner scanner = new Scanner(System.in);

double a=scanner.nextDouble();
double c=a*2*3.14;
	System.out.println(c);
}
	  }