using System;
using System.Collections.Generic;
using System.Linq;

public class Test
{
	public static void Main()
	{
	    var strings = new[]{ "hi", "hey", "hi", "hi" };
        string first = strings.FirstOrDefault(s => s != "N/A");
        bool allEqual = first == null ||  strings.All(s => s == "N/A" || s == first);
        Console.Write("are all strings equal? " + allEqual);
	}
}