Given the following data, what is the exponential smoothing forecast with $a=2$ for period $4?$ Use a naive forecast as your starting point.

Month Demand

$1=19$

$2=20$

$3=18$

$4,19$

$5,17$

$18\mathrm{.}58$

$18\mathrm{.}96$

$19$

$19\mathrm{.}2$