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

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            double c = double.Parse(Console.ReadLine());
            double[] x = Console.ReadLine().Split().Select(double.Parse).ToArray();
            double kirikuti = (x[1] - x[0]) / 2;
            kirikuti *= kirikuti;
            kirikuti *= Math.PI;
            double syuu = (x[0] + x[1]) * Math.PI;
            Console.WriteLine(kirikuti * syuu * c);
        }
    }
}