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.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.text.DecimalFormat;
import java.util.Scanner;

public class justForFun {

	static Scanner sc=new Scanner(System.in);
	static StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
	static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));

	public static void main(String[] args) throws IOException {
		double PI=Math.PI;
		double n=nextDouble();
		double r=nextDouble();
		double ang1=PI/2/n;
		double ang2=PI/n;
		double ang3=PI-ang1-ang2;
		double x=r*Math.sin(ang2)/Math.sin(ang3);
		double s=Math.sin(ang1)*x*r*n;
		DecimalFormat df=new DecimalFormat("0.########");
		out.println(df.format(s));
		out.flush();
	}
	
	static String next() throws IOException{
		in.nextToken();
		return in.sval;
	}

	static int nextInt() throws IOException {
		in.nextToken();
		return (int) in.nval;
	}

	static double nextDouble() throws IOException {
		in.nextToken();
		return in.nval;
	}

	static long nextLong() throws IOException {
		in.nextToken();
		return (long) in.nval;
	}
	
	static long C(long n,long m){
		long res=n-m;
		if(res>n/2)
			res=m;
		long fenzi=1;
		long fenmu=1;
		for(long i=1;i<=res;i++){
			fenzi*=n--;
			fenmu*=i;
		}
		return fenzi/fenmu;
	}
	
	static long A(long n,long m){
		long ans=1;
		for(long i=n-m+1;i<=n;i++){
			ans*=i;
		}
		return ans;
	}
}