# Zju2253 Fill the Grid

时间限制：1s 空间限制：128MB

### 题目描述

Given an m*n grid, you're required to fill it with the numbers from 1 to m*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*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.

### 样例输入

2 3 0 0

### 样例输出

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