March 8#2293
March 8 is approaching, and Vasya wants to congratulate his mother with a bouquet of flowers. Since Vasya's mother is a mathematics teacher, it is natural that Vasya is interested in mathematical problems. This time, he is thinking about the following question: if Vasya grows different types of flowers in his home greenhouse, in how many different ways can he create a bouquet for his mother?
Vasya considers a bouquet to be a set of at least three flowers. In addition, Vasya understands that on March 8 you can only give a bouquet with an odd number of flowers.
The single line contains a natural number (N \leq 21).
Output a single number — the number of different bouquets Vasya can make.
Example 1