The five most important numbers in maths

Euler got joining the five most important numbers in maths in an equation:

$e^{i \cdot \pi}$ +1 = 0.

Mathematicians were very proud with this formula until the early 20th century when the crisis arose the basics. It was necessary reformulate the theory of sets to avoid paradoxes, but this is another history. Ok, let's go. How may solutions (not necessarily real solutions) does the next equation have?

$e^{x}$ +1 = 0