时间限制：C/C++/Rust/Pascal 2秒，其他语言4秒
空间限制：C/C++/Rust/Pascal 512 M，其他语言1024 M
64bit IO Format: %lld
空间限制：C/C++/Rust/Pascal 512 M，其他语言1024 M
64bit IO Format: %lld
题目描述
Bobo has a string of length 2(n + m) which consists of characters `A` and `B`. The string also has a fascinating property: it can be decomposed into (n + m) subsequences of length 2, and among the (n + m) subsequences n of them are `AB` while other m of them are `BA`.
Given n and m, find the number of possible strings modulo)
.
Given n and m, find the number of possible strings modulo
输入描述:
The input consists of several test cases and is terminated by end-of-file.
Each test case contains two integers n and m.
*
* There are at most 2019 test cases, and at most 20 of them has.
输出描述:
For each test case, print an integer which denotes the result.