The Subset

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Points: 20 (partial)
Time limit: 1.0s
Memory limit: 512M

Problem types

Given the first N positive integers, there are 2N1 non-empty subsets. Bob wants to choose M distinct subsets from them so that each integer in the union of the M subsets occurred an even number of times. For example, if N=3 and M=3, there are 7 non-empty subsets. Bob can choose the subsets {1}, {2}, and {1,2}, where every integer has an even number of occurences. Can you help Bob to find the number of different ways to choose the M subsets? Since the answer is huge, ouptut the answer modulo 109+7.

Input Specification

The first line of input contains two integers N and M (N,M106).

Output Specification

Output one integer, the number of ways to choose subsets.

Constraints

Subtask Points Additional constraints
1 20 N,M5.
2 30 N,M3000.
3 50 No additional constraints.

Sample Input 1

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3 3

Sample Output 1

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7

Explanation

There are 7 ways to choose 3 subsets, listed as following:

  • {1}, {2}, {1,2}
  • {1}, {3}, {1,3}
  • {2}, {3}, {2,3}
  • {1}, {2,3}, {1,2,3}
  • {2}, {1,3}, {1,2,3}
  • {3}, {1,2}, {1,2,3}
  • {1,2}, {2,3}, {1,3}

Sample Input 2

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5 3

Sample Output 2

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155

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