fibExponential = n =>
  n < 2 ? n : fibExponential(n - 1) + fibExponential(n - 2)
Regular fibonacci implementation following the definition:
Fib(0) = 0
Fib(1) = 1
Fib(n) = Fib(n-1) + Fib(n-2)

@param Number
@return Number