/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
			Scanner sc = new Scanner(System.in); 
	        int n;
	        double x;
	        n = sc.nextInt();
            x = sc.nextInt();	       
	        double result=0;
	        for(int i = n; i > 0; i--){
	        	int j = 1;
				if((i%2)==0) j = -1;
				result += j * Math.sin(i * x) / i;
			}
			System.out.println(result);
	}
}