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문제

Vera has a grid with H rows and N columns. Rows are numbered 1 to H and columns are numbered 1 to N. Let the cell in the r-th row and c-th column be (r, c). Cells are coloured white or black. A colouring is a pyramid if:

  • Exactly N cells are black.
  • (1, 1) is black.
  • If (r, a) and (r, b) are black, then (r, k) is black for a < k < b.
  • If (r, c) is black, then (r − 1, c), if it exists, is black.
  • If (r, c) is black and there is no k < c such that (r, k) is black, then (r + 1, c), if it exists, is white.

Two pyramids are different if there is a cell that is white in one pyramid and black in the other. Compute the number of different pyramids modulo 109 + 7.

입력

Line 1 contains integers H and N (1 ≤ H, N ≤ 105).

출력

Print one line with one integer, the number of different pyramids modulo 109 + 7.

예제 입력 1

2 6

예제 출력 1

7

예제 입력 2

3 20

예제 출력 2

487

힌트

For the first example, the seven pyramids are:

###### ####.. ####.. #####. #####. #####. #####.
...... .##... ..##.. .#.... ..#... ...#.. ....#.