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

$\backslash$table$[[$Month$,$Demand$],[1,19],[2,20],[3,18],[4,19],[5,17]]$

$2\mathrm{.}25$

$338$

$1\mathrm{.}58$

$291$