shunfurh
编程介的小学生
2017-09-24 16:08

Harry And Magic Box

  • box
  • it
  • each

Problem Description
One day, Harry got a magical box. The box is made of n*m grids. There are sparking jewel in some grids. But the top and bottom of the box is locked by amazing magic, so Harry can’t see the inside from the top or bottom. However, four sides of the box are transparent, so Harry can see the inside from the four sides. Seeing from the left of the box, Harry finds each row is shining(it means each row has at least one jewel). And seeing from the front of the box, each column is shining(it means each column has at least one jewel). Harry wants to know how many kinds of jewel’s distribution are there in the box.And the answer may be too large, you should output the answer mod 1000000007.

Input
There are several test cases.
For each test case,there are two integers n and m indicating the size of the box. 0≤n,m≤50.

Output
For each test case, just output one line that contains an integer indicating the answer.

Sample Input
1 1
2 2
2 3

Sample Output
1
7
25

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