P13938 [EC Final 2019] City

Hi ICPCer, welcome to Xi'an. Being a beautiful ancient city, Xi'an is the capital city of Zhou, Qin, Han, and Tang Dynasties. With a long history, the streets in Xi'an have a grid pattern. Attracted by the streets' structure, Coach $\textit{Pang}$ would like to conduct his research on them. He draws an $n\times m$ grid on the board. The grid consists $n+1$ vertical line segments and $m+1$ horizontal line segments. The vertical and horizontal line segments intersect at exactly $(n+1)\times(m+1)$ points, forming $n\times m$ unit squares. We call the $(n+1)\times (m+1)$ intersections $\textit{grid point}$s. Output the number of line segments(not only vertical or horizontal) $l$ satisfying the following three conditions: - The length is not zero. - Both endpoints of $l$ are grid points. - The midpoint of $l$ is a grid point.

The only line contains two integers $n, m$($1\le n, m\le 1000$).

Print the answer in a single line.