Transformations

Consider a sequence of one bit "0". N continue to perform the following steps. At each step, bit "0" is replaced by two bits "10", and bit "1" two bits "01". After the first step of a sequence of "0" is a sequence of "10", after the second – "0110", after the third – "10010110", after the fourth – "0110100110010110", and so on.

Write a program that determines the number of neighboring bits "00" in sequence after the N-th step.

Input

We introduce a single integer N (1  ≤  N  ≤  1000).

Output

Display the number of neighbors "00" after the N-th step.

Examples