import java.util.Scanner;

public class Main {	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	}

} import java.util.Scanner; Scanner java.util public class Main {	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	} main {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int R = sc.nextInt(); R sc.nextInt() sc.nextInt sc double r = 2*(3.14159265)*R; r 2*(3.14159265)*R 2*(3.14159265)*R 2 (3.14159265) R System.out.println(r) System.out.println System.out System System.out r String[] args args public class Main {	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	}

} public class Main {	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	}

} Main
import java.util.Scanner;

public class Main {	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int R = sc.nextInt();
		
		double r = 2*(3.14159265)*R;
		
		System.out.println(r);
	}

}