  In this paper, we propose a semi-discrete first-order low regularity
exponential-type integrator (LREI) for the ``good" Boussinesq equation. It is
shown that the method is convergent linearly in the space $H^r$ for solutions
belonging to $H^{r+p(r)}$ where $0\le p(r)\le 1$ is non-increasing with respect
to $r$, which means less additional derivatives might be needed when the
numerical solution is measured in a more regular space. Particularly, the LREI
presents the first-order accuracy in $H^{r}$ with no assumptions of additional
derivatives when $r>5/2$. This is the first time to propose a low regularity
method which achieves the optimal first-order accuracy without loss of
regularity for the GB equation. The convergence is confirmed by extensive
numerical experiments.
