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);