C# Generate a random number without any function

I need to generate a random number between 85 and 90 without using any functions. How about creating an array and adding the numbers into that array? But how do I pick a random number from this string? Do you have a different suggestion? Shouldn't be with a class.

int [] numbers = new int[6] { 85, 86, 87, 88, 89, 90};

Thanks.