Given a string `word`, return the sum of the number of vowels (`'a'`, `'e'`, `'i'`, `'o'`, and `'u'`) in every substring of `word`.

A substring is a contiguous (non-empty) sequence of characters within a string.

Note: Due to the large constraints, the answer may not fit in a signed 32-bit integer. Please be careful during the calculations.

Example 1:

    Input: word = "aba"
    Output: 6
    Explanation:
    All possible substrings are: "a", "ab", "aba", "b", "ba", and "a".
    - "b" has 0 vowels in it
    - "a", "ab", "ba", and "a" have 1 vowel each
    - "aba" has 2 vowels in it
    Hence, the total sum of vowels = 0 + 1 + 1 + 1 + 1 + 2 = 6.

Example 2:

    Input: word = "abc"
    Output: 3
    Explanation:
    All possible substrings are: "a", "ab", "abc", "b", "bc", and "c".
    - "a", "ab", and "abc" have 1 vowel each
    - "b", "bc", and "c" have 0 vowels each
    Hence, the total sum of vowels = 1 + 1 + 1 + 0 + 0 + 0 = 3.

Example 3:

    Input: word = "ltcd"
    Output: 0
    Explanation: There are no vowels in any substring of "ltcd".

Constraints:

- `1 <= word.length <= 105`
- `word` consists of lowercase English letters.