using System;

public class Program

{

    public static void Main()

    {

double y1=0;

double y2=0;

double i2=0;

double p1=0;

double p2=0;

double pi=0;

double podzial=double.Parse(Console.ReadLine());

double r=double.Parse(Console.ReadLine());

double i=(-r);

while (i<r)

{

y1=Math.Sqrt(r*r-(i*i));

i2=i+(r/podzial);

y2=Math.Sqrt(r*r-((i2*i2)));

p1=((y1+y2)*(r/podzial))/2;

p2=p2+p1;

i= i+(r/podzial);

}

pi=(2*p2)/(r*r);

Console.WriteLine ("{0}",pi);

    }

}