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 (x1,y1), (x2,y2), ..., (xn,yn). The first vertex has a coordinate x1=1, the second - x2=2, etc. Coordinates yi might be any, but should satisfy the following conditions:
there should be t humps precisely, i.e. such indexes j (2 \le j \le n-1), so that yj-1 \lt yj \gt yj+1, there should be precisely t-1 such indexes j (2 \le j \le n-1), so that yj-1 \gt yj \lt yj+1, no segment of a polyline should be parallel to the Ox-axis, all yi 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.

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

Output the required amount of camels with t humps.

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