import java.util.*;
import java.lang.Math;

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

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