Problem: It was decided in IT City to distinguish successes of local IT companies by awards in the form of stars covered with gold from one side. To order the stars it is necessary to estimate order cost that depends on the area of gold-plating. Write a program that can calculate the area of a star.

A "star" figure having n ≥ 5 corners where n is a prime number is constructed the following way. On the circle of radius r n points are selected so that the distances between the adjacent ones are equal. Then every point is connected by a segment with two maximally distant points. All areas bounded by the segments parts are the figure parts.

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Input

The only line of the input contains two integers n (5 ≤ n < 109, n is prime) and r (1 ≤ r ≤ 109) — the number of the star corners and the radius of the circumcircle correspondingly.

Output

Output one number — the star area. The relative error of your answer should not be greater than 10 - 7.

Examples

Input

7 10


Output

108.395919545675

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.StringTokenizer;

public class Main 
{
	public static void main(String[] args) 
	{
		InputReader in = new InputReader();
//		Scanner in=new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		while(in.hasNext())
		{
			int n=in.nextInt();
			int r=in.nextInt();
			double j7=0.5*(180.0/n);
			double j6=180.0/n;
			double j8=180-j6-j7;
//			System.out.println(j6+" "+j7+" "+j8);
			double a1=r*Math.sin(j7*Math.PI/180.0)/Math.sin(j8*Math.PI/180.0);
//			double b1=r*Math.sin(j6*Math.PI/180.0)/Math.sin(j8*Math.PI/180.0);
			double S=0.5*a1*r*Math.sin(j6*Math.PI/180.0);
//			double p=(r+a1+b1)/2.0;
//			double S=Math.sqrt(p*(p-r)*(p-a1)*(p-b1));
			out.println(S*2.0*n);
//			System.out.println(hu);
//			double rr=180*hu/(j6*Math.PI);
//			System.out.println(rr);
//			double S=hu*rr/2.0;
//			out.println(Math.PI*r*r-n*S);
		}
		out.close();
	}
}

class InputReader 
{
	BufferedReader buf;
	StringTokenizer tok;
	InputReader() 
	{
		buf = new BufferedReader(new InputStreamReader(System.in));
	}

	boolean hasNext() 
	{
		while (tok == null || !tok.hasMoreElements()) 
		{
			try 
			{
				tok = new StringTokenizer(buf.readLine());
			} 
			catch (Exception e) 
			{
				return false;
			}
		}
		return true;
	}

	String next() 
	{
		if (hasNext())
			return tok.nextToken();
		return null;
	}

	int nextInt() 
	{
		return Integer.parseInt(next());
	}

	long nextLong() 
	{
		return Long.parseLong(next());
	}

	double nextDouble() 
	{
		return Double.parseDouble(next());
	}

	BigInteger nextBigInteger() 
	{
		return new BigInteger(next());
	}

	BigDecimal nextBigDecimal() 
	{
		return new BigDecimal(next());
	}
}