using System;

public class Hello
{
    public static void Main()
    {
        var c = int.Parse(Console.ReadLine().Trim());
        if (c == 0) { Console.WriteLine(0); goto end; }
        string[] line = Console.ReadLine().Trim().Split(' ');
        var rin = int.Parse(line[0]);
        var rout = int.Parse(line[1]);
        var ans = (rout - rin) * (rout - rin) * Math.PI * Math.PI * (rout + rin) * c / 4d;
        Console.WriteLine(ans);
        end:;
    }
}