Description

There is a Wcm x Hcm paper grid. Each grid is 1cm x 1cm. Suppose that you were going to cut out and use each of the 1cm x 1cm square grid, but someone cut the paper diagonally so you now have two right-triangle paper pieces. You don’t have another piece of grid paper, so you decide to use the two triangle paper pieces.
Given W and H, write a solution function that returns the number of 1 x 1 squares that you can use.

Constraints
  • W and H are integers. 1 ≤ W, H ≤ 100,000,000

Example

W H result
8 12 80

Example #1

The size of the paper board is 8 x 12. With this rectangle, you can make 96 squares. But, by cutting the paper board diagonally, 16 squares turns into 32 triangles. So you can get (96 - 16 = 80) squares.

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