题目描述

Given an $m \times n$ grid, you're required to fill it with the numbers from $1$ to $m \times n$ but the following rules should be satisfied:

1. each number in grid is larger than its above;
2. each number in grid is larger than its left.

Now, I wonder how many distinct solutions I could make on a grid.
For example. Consider such a $2 \times 3$ grid, we have the following solutions:
123 124 134 135 125
456 356 256 246 346
Thus, the sum is $5$.

输入格式

Two positive integer $m, n (0 < m, n < 10)$ per line. Two zeros indicate the end of input.

输出格式

A single integer per line for each case -- the number of distinct solutions.

2 3
0 0

5

提示

本题为多组数据，请做到 0 0 结束。

题目来源

没有写明来源。