Employees
At the factory each of the N items can be processed in one of two machines: A or B. Each piece has a serial number from 1 to N. The processing of parts after the other, in accordance with their numbers. Amount of detail is always even.
There are rules under which determines whether you can handle detail on a particular machine.
If currently on the machine B was processed the same number of parts, as well as on the machine A, then the next part must be machined A.
In sum, in each of the machines should be treated the same amount of detail.
How many people, so many opinions. Each of the employees of this plant has offered a sequence of machining, all proposals have been different, but those that satisfy rules 1 and 2.
Write a program that according to information on the number of parts N determines the maximum number of factory workers.
Input
One even integer N (2 ≤ N ≤ 28) - the amount of details to be processed.
Output
Print one integer - the maximum number of factory workers.