Implicit casting of Null-Coalescing operator result

Question

With the following understanding about null coalescing operator (??) in C#.

int? input = -10;
int result = input ?? 10;//Case - I
//is same as:
int result = input == null? input : 10; // Case - II

While, by definition and usage, Case I and Case II are same.

It is surprising to see that in Case-I compiler is able to implicitly cast int? to int while in Case-II it shows error: 'Error 1 Cannot implicitly convert type 'int?' to 'int'"

What is it that I am missing about null-coalescing operator?

Thanks for your interest.