import java.util.Scanner;
 
public class Main{
 
	public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	}
} import java.util.Scanner; Scanner java.util public class Main{
 
	public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	}
} Main public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	} main {
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int R = scan.nextInt(); R scan.nextInt() scan.nextInt scan double result = R*2*3.1415; result R*2*3.1415 R*2*3.1415 R 2 3.1415 scan.close() scan.close scan System.out.println(result) System.out.println System.out System System.out result String args[] args public class Main{
 
	public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	}
} public class Main{
 
	public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	}
} Main
import java.util.Scanner;
 
public class Main{
 
	public static void main(String args[]){
		Scanner scan = new Scanner(System.in);
		int R = scan.nextInt();
		double result = R*2*3.1415;
		scan.close();
		System.out.println(result);
	}
}