You are given a string s consisting of lowercase English letters and digits.

Each character has a corresponding mirror character:

• For lowercase English letters, the $i^{ ext{th}}$ letter from the beginning of the alphabet is paired with the $i^{ ext{th}}$ letter from the end of the alphabet (such that 'a' pairs with 'z', 'b' pairs with 'y', and so on up to 'm' pairing with 'n').

• For digits, each digit $d$ is paired with the digit $9 - d$ (such that '0' pairs with '9', '1' pairs with '8', and so on up to '4' pairing with '5').

For every unique mirror pair $(c, m)$, let freq(c) and freq(m) denote the number of occurrences of characters $c$ and $m$ in s respectively.

Return the sum of $| ext{freq}(c) - ext{freq}(m) |$ across all mirror pairs.

Constraints:

• $1 \leq$ s.length $\leq 5 imes 10^5$

• s consists only of lowercase English letters and digits.

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