Count Strings with At Least One 'X'

You are given a non-negative integer N, and you need to calculate the number of distinct strings of length N formed using the characters 'X' and 'Y' that contain at least one 'X'.

Every string created without any restrictions would have a total of $2^N$ possibilities (since for each position there are 2 choices). However, the string which consists entirely of 'Y's does not meet the requirement. Hence, the answer is given by the formula:

$2^N - 1$

If N is 0, there are no characters to form a string and thus the answer is 0.

inputFormat

The input is provided via standard input and consists of a single integer N where N is a non-negative integer.

outputFormat

Output a single integer that represents the number of distinct strings of length N consisting of 'X' and 'Y' that contain at least one 'X'.

1

1