using System;
using System.Linq;

class Program
{
    static void Main()
    {
        double c = double.Parse(Console.ReadLine());
        double[] r = Console.ReadLine().Split().Select(double.Parse).ToArray();

        Console.WriteLine(c * (r[0] + r[1]) * Math.Pow((r[1] - r[0]) * Math.PI / 2, 2));
    }
}