Minimum Deletions for Alternating Characters

Given a string s consisting solely of the characters 'a' and 'b', your task is to determine the minimum number of deletions required so that the resulting string is alternating. A string is called alternating if no two adjacent characters are the same.

You can express the required number of deletions mathematically as:

$$ D = \sum_{i=1}^{n-1} \mathbf{1}\{s_i = s_{i+1}\} $$

where \(s_i\) represents the i-th character of the string and \(\mathbf{1}\{\cdot\}\) is the indicator function, which is 1 if the condition inside is true and 0 otherwise.

inputFormat

The input is provided via stdin and consists of a single line containing a non-empty string s that is composed only of the characters 'a' and 'b'.

outputFormat

Output to stdout a single integer representing the minimum number of deletions required to make the string alternating.

aab

1