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1 초 128 MB31242175.000%

## 문제

Count the number of permutations that have a specific number of inversions.

Given a permutation a1a2a3,..., an of the n integers 1, 2, 3, ..., n, an inversion is a pair (aiaj) where i < j and ai > aj. The number of inversions in a permutation gives an indication on how "unsorted" a permutation is. If we wish to analyze the average running time of a sorting algorithm, it is often useful to know how many permutations of n objects will have a certain number of inversions.

In this problem you are asked to compute the number of permutations of n values that have exactly k inversions.

For example, if n = 3, there are 6 permutations with the indicated inversions as follows:

 123 0 inversions 132 1 inversion (3 > 2) 213 1 inversion (2 > 1) 231 2 inversions (2 > 1, 3 > 1) 312 2 inversions (3 > 1, 3 > 2) 321 3 inversions (3 > 2, 3 > 1, 2 > 1)

Therefore, for the permutations of 3 things

• 1 of them has 0 inversions
• 2 of them have 1 inversion
• 2 of them have 2 inversions
• 1 of them has 3 inversions
• 0 of them have 4 inversions
• 0 of them have 5 inversions
• etc.

## 입력

The input consists one or more problems. The input for each problem is specified on a single line, giving the integer n (1 <= n <= 18) and a non-negative integer k (0 <= k <= 200). The end of input is specified by a line with n = k = 0.

## 출력

For each problem, output the number of permutations of {1, ..., n}with exactly k inversions.

## 예제 입력 1

3 0
3 1
3 2
3 3
4 2
4 10
13 23
18 80
0 0


## 예제 출력 1

1
2
2
1
5
0
46936280
184348859235088