Array Swaps

Salmon received an array $A$ of size $N$ and an array $B$ of size $M$ for Christmas. He would like to move all the elements in $B$ to $A$ using a special method described below. While $B$ is not empty, Salmon does the following operations in order: * Remove and store the leftmost element off of B (let's call this element $X$). * Place $X$ at the start of $A$. * Keep swapping $X$ and the element