Given two strings $A$ and $B$ with the same length and composed of uppercase English letters, ensure that each letter in $A$ and $B$ appears the same number of times.You can exchange two adjacent characters in string $A$ each time, find out how many times you need to exchange so that string $A$ becomes string $B$.

The first line is a positive integer $N \ (2≤N≤10^6)$, which represents the length of the string.The second and third lines each have a string of length $N$ , which represent sting $A$ and string $B$ and contain only uppercase letters.

A nonnegative integer that represents the minimum number of exchanges.