C# Fundamentals - Magic Letters Combinations

using System;
class Program
{
    static void Main()
    {
        char firstChar = char.Parse(Console.ReadLine().ToLower());
        char secondChar = char.Parse(Console.ReadLine().ToLower());
        char mustMissThatChar = char.Parse(Console.ReadLine().ToLower());

        for (char i = firstChar; i <= secondChar; i++)
        {
            for (char j = firstChar; j <= secondChar; j++)
            {
                for (char k = firstChar; k <= secondChar; k++)
                {
                    if (!(i == mustMissThatChar || j == mustMissThatChar || k == mustMissThatChar))
                    Console.Write("{0}{1}{2} ", i, j, k);
                }
            }
        }
    }
}