[讨论]ZJU2284何解

Inversion Number

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Time limit: 1 Seconds Memory limit: 32768K
Total Submit: 842 Accepted Submit: 335

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Let { A1,A2,...,An } be a permutation of the set{ 1,2,..., n}. The inversion number of the permutation is the number of integer pairs (i,j) that satisfy 1<=i<j<=n and Ai>Aj.

Your task is to calculate how many n-permutations has an inversion number of k.

Input

The input consists of several test cases. Each test case contains two integers n(0<n<=20) and k(0<=k<=200), which are mentioned above. Input is terminated by n=m=0, which should not be proceeded.

Output

For each case of input output the number of n-permutations that has an inversion number of k in one line.

Sample Input

2 0
5 3
0 0

Sample Output

1
15

没怎么看懂题