Bob likes to draw camels: with a single hump, two humps, three humps, etc. He draws a camel by connecting points on a coordinate plane. Now he's drawing camels with t humps, representing them as polylines in the plane. Each polyline consists of n vertices with coordinates (x 1, y 1), (x 2, y 2), ..., (x n , y n ). The first vertex has a coordinate x 1 = 1, the second — x 2 = 2, etc. Coordinates y i might be any, but should satisfy the following conditions: there should be t humps precisely, i.e. such indexes j (2 ≤ j ≤ n - 1), so that y j - 1 y j y j + 1 , there should be precisely t - 1 such indexes j (2 ≤ j ≤ n - 1), so that y j - 1 y j y j + 1 , no segment of a polyline should be parallel to the Ox -axis, all y i are integers between 1 and 4. For a series of his drawings of camels with t humps Bob wants to buy a notebook, but he doesn't know how many pages he will need. Output the amount of different polylines that can be drawn to represent camels with t humps for a given number n .

输入描述:

The first line contains a pair of integers n and t (3 ≤ n ≤ 20, 1 ≤ t ≤ 10).

输出描述:

Output the required amount of camels with t humps.

备注:

In the first sample test sequences of y-coordinates for six camels are: 123421, 123431, 123432, 124321, 134321 и 234321 (each digit corresponds to one value of yi).