题目描述

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

2 3
0 0

5

f提示 本题为多组数据，请做到"0 0"结束

Source