Problem Statement

A string, consisting of letters A, B, and C, is called good, if every two consecutive letters are different. For example, strings ABABAB and ABC are good, while ABBA and AABBCC aren't.
You are given two good strings S and T of length N.
In one operation, you can choose any letter of S, and change it to another letter among A, B, and C, so that S remains good.
What's the smallest number of operations needed to transform S into T?
We can prove that it can always be done in a finite number of operations.

Input

Input is given from Standard Input in the following format:
N
S
T

Output

Output the smallest number of operations needed to transform S into T.

Constraints

• $1\le N \le 5\cdot 10^5$
• S is a good string of length N consisting of A, B, and C
• T is a good string of length N consisting of A, B, and C

Sample Input 1

4
CABC
CBAC

Sample Output 1

6

Here is one possible sequence of operations of length 6:
CABC $\to$ BABC $\to$ BCBC $\to$ BCAC $\to$ ACAC $\to$ ABAC $\to$ CBAC
It can be shown that 6 operations are necessary for this case.

Sample Input 2

10
ABABABABAB
BABABABABA

Sample Output 2

15

见题面 Input 部分

见题面 Output 部分