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## 문제

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 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 grid points. Output the number of line segments(not only vertical or horizontal) $l$ satisfying the following three conditions:

1. The length is not zero.
2. Both endpoints of $l$ are grid points.
3. The midpoint of $l$ is a grid point.

## 입력

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

## 출력

Print the answer in a single line.

## 예제 입력 1

1 1


## 예제 출력 1

0


## 예제 입력 2

2 3


## 예제 출력 2

14