public class MessageBox                                                    
{                                    
    private Stack<string> messages = new Stack<string>();        
    public int MessageCount { get { return messages.Count; } } 

    public void AddMessage(string message)
    {
        messages.Push(message);
    }
 
    public int FindMessage(string message)
    {
        for (var i = 0; i < messages.Count(); i++)
        {
            if (messages.ElementAt(i) == message)
            {
                return i;               
            }
        }
        return -1;
    }

    public void RemoveMessage(string message)
    {
        var temp = new Stack<string>();
      
        var i = FindMessage(message);

        if (i > -1)
        {
            for (var j = (messages.Count - 1); j >= 0; j--)
            {
                if (j != i )
                {
                    var msg = messages.ElementAt(j);
                    temp.Push(msg); 
                }
            }

            messages.Clear();

            messages = temp;     
        }
    }

    public override string ToString()
    {
        var sb = new System.Text.StringBuilder();
        foreach(var s in messages)
        {
            sb.Append(s);
            sb.Append('\n');
        }
        return sb.ToString();
    }
}