import java.util.*;
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int b=sc.nextInt();
		System.out.println(b*2*3.14);
		
		
	}

} import java.util.*; util.* java public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int b=sc.nextInt();
		System.out.println(b*2*3.14);
		
		
	}

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

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int b=sc.nextInt();
		System.out.println(b*2*3.14);
		
		
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int b=sc.nextInt();
		System.out.println(b*2*3.14);
		
		
	}

} Main
import java.util.*;
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int b=sc.nextInt();
		System.out.println(b*2*3.14);
		
		
	}

}
