My Derivative Is Myself

Calculus Level 1

How many functions are there such that $f(x) = f'(x)$ ?

Clarification: While functions such as $f(x)=2^{x}$ and $f(x)=2^{x+1}$ are in the same family of functions, they are different functions, so if you found those two as the only answers, your answer would be 2.