Problem Statement

You are given two strings $S$ and $T$ of length $N$ consisting of A and B. Let $S_i$ denote the $i$-th character from the left of $S$.

You can repeat the following operation any number of times, possibly zero:

• Choose integers $i$ and $j$ such that $1\leq i < j \leq N$. Replace $S_i$ with A and $S_j$ with B.

Determine if it is possible to make $S$ equal $T$. If it is possible, find the minimum number of operations required.

Constraints

• $2 \leq N \leq 2 \times 10^5$
• Each of $S$ and $T$ is a string of length $N$ consisting of A and B.
• All input numbers are integers.

Input

The input is given from Standard Input in the following format:

N
S
T

Output

If it is impossible to make $S$ equal $T$, print -1.

Otherwise, print the minimum number of operations required to do so.