using System;
using System.Collections.Generic;
using System.Linq;

public class Yuki89
{
	public static void Main()
	{
		var c = double.Parse(Console.ReadLine());
		var r = Console.ReadLine().Split(' ').Select(x => double.Parse(x)).ToList();
		Console.WriteLine(c * 1 / 4 * Math.PI * Math.PI * (r[0] + r[1]) * (r[1] - r[0]) * (r[1] - r[0]));
	}
}