Count Missing Numbers

Create a function that takes a list of "mostly" numbers, counts the amount of missing numbers and returns their sum. Watch out for strings!

Examples

count_missing_nums(["1", "3", "5", "7", "9"]) ➞ 4
# 1+1+1+1

count_missing_nums(["7", "3", "1", "9", "5"]) ➞ 4

count_missing_nums(["1", "5", "B", "9", "z"]) ➞ 6

Notes

The data might be dirty! Clean out any filthy strings.