Create a C# program that simulates a simple English to Spanish dictionary. You should use a dictionary collection to store the English words as keys and their corresponding Spanish translations as values. The program should allow users to input an English word, and the program should output its Spanish translation. If the word does not exist in the dictionary, it should output a message indicating that the word is not found.

Here's a simple C# program that simulates an English to Spanish dictionary:

```csharp
using System;
using System.Collections.Generic;

class Program
{
static void Main()
{
Dictionary<string, string> dictionary = new Dictionary<string, string>();
dictionary.Add("hello", "hola");
dictionary.Add("goodbye", "adiós");
dictionary.Add("apple", "manzana");
dictionary.Add("cat", "gato");

Console.WriteLine("Welcome to the English to Spanish dictionary!");

while (true)
{
Console.Write("Enter an English word to translate to Spanish (or 'exit' to quit): ");
string input = Console.ReadLine();

if (input.ToLower() == "exit")
{
Console.WriteLine("Goodbye!");
break;
}

if (dictionary.ContainsKey(input))
{
Console.WriteLine($"{input} in Spanish is: {dictionary[input]}");
}
else
{
Console.WriteLine("Word not found in the dictionary.");
}
}
}
}
```

This program creates a dictionary with English words as keys and their corresponding Spanish translations as values. It then prompts the user to enter an English word and translates it to Spanish if it exists in the dictionary. The user can type "exit" to quit the program.