import java.util.Scanner;

public class Main
{
	public static void main (String[] args)
	{
		int n, powOf2 = 1;
		double x, sum = 0;
		Scanner scanner = new Scanner(System.in);
		
		n = scanner.nextInt();
		x = scanner.nextDouble();
		
		for (int i = 1; i <= n; i++)
		{
			powOf2 *= 2;
			sum += Math.sin(i*x)/powOf2;
		}
		
		System.out.println(sum);
	}
}