C# Magic Letter - Second Solution

namespace RevisonSomething
{
    using System;
    public class Program
    {
        static void Main()
        {
            char firstLetter = char.Parse(Console.ReadLine());
            char secondLetter = char.Parse(Console.ReadLine());
            string skipLetter = Console.ReadLine();

            for (char i = firstLetter; i <= secondLetter; i++)
            {
                for (char j = firstLetter; j <= secondLetter; j++)
                {
                    for (char k = firstLetter; k <= secondLetter; k++)
                    {
                        string input = $"{i}{j}{k} ";
                        if (!input.Contains(skipLetter))
                        {
                            Console.Write(input);
                        }
                    }
                }
            }
        }
    }
}