  For an irrational number $x\in [0,1)$, let $x=[a\_1(x), a\_2(x),\cdots]$ be
its continued fraction expansion. Let $\psi : \mathbb{N} \rightarrow
\mathbb{N}$ be a function with $\psi(n)/n\to \infty$ as $n\to\infty$. The
(upper, lower) fast Khintchine spectrum for $\psi$ is defined as the Hausdorff
dimension of the set of numbers $x\in (0,1)$ for which the (upper, lower) limit
of $\frac{1}{\psi(n)}\sum\_{j=1}^n\log a\_j(x)$ is equal to $1$. The fast
Khintchine spectrum was determined by Fan, Liao, Wang, and Wu. We calculate the
upper and lower fast Khintchine spectra. These three spectra can be different.
