Given a string S consisting of N letters a and b. In one move you can replace one letter by the other (a by b or b by a).

Write a function solution that given such a string S, returns the minimum number of moves required to obtain a string containing no instances of three identical consecutive letters.

#Example 1:

Input: "baaaaa"
Output: 1
Explanation: The string without three identical consecutive letters which can be obtained is one move is "baabaa".

Example 2:
Input: "baaabbaabbba"
Output: 2
Explanation: There are four valid strings obtainable in two moves, for example "bbaabbaabbaa".

Example 3:
Input: "baabab"
Ouput: 0

Assumptions:
N is an integer within the range [0, ..200,000];
string S consists of only characteres a and b*