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排列组合

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 8761    Accepted Submission(s): 3618


Problem Description
有n种物品，并且知道每种物品的数量。要求从中选出m件物品的排列数。例如有两种物品A,B，并且数量都是1，从中选2件物品，则排列有"AB","BA"两种。
 

Input
每组输入数据有两行，第一行是二个数n,m(1<=m,n<=10)，表示物品数，第二行有n个数，分别表示这n件物品的数量。
 

Output
对应每组数据输出排列数。(任何运算不会超出2^31的范围)
 

Sample Input
2 2
1 1
 

Sample Output
2
 

Author
xhd
 

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