March 8

March Eighth already near and Vasya plans to congratulate my mother bouquet of flowers. Since mom Vasja teacher and also mathematics, it is natural that Vasya primarily interested in mathematical problems. This time he is interested in the question follows: how many ways he can make a bouquet for mom, if your home greenhouse growers Vasya N different types of flowers. Vasya finds a bouquet of a set of at least three colors. In addition Vasya has grown up and understands that on March 8 can give a bouquet of only an odd number of flowers.

Input

The single line of input contains an integer N (N ≤ 21).

Output

Derive a single number - the number of different bouquets, which can generate Vasya.

Examples