Inversions 
Time limit:  1.00 s 
Memory limit:  512 MB 

You are given a bit string, and your task is to modify it so that no adjacent bits have the same value. On each turn, you may select any bit and
invert it (from 0 to 1 or from 1 to 0). What is the minimum number of inversions if you act optimally?
Input
The only input line has a bit string of length $n$.
Output
Print one integer: the minimum number of inversions.
Constraints
Example
Input:
011001
Output:
2
Explanation: You can invert the third and fourth bit, and the resulting string is 010101.