Determine the date in the month, 1..31, of the nth weekday.
year
month, 1..12
day of week 0..6 representing Sunday..Saturday
nth occurrence of that weekday in the month, 1..5, where 5 also means "the last occurrence in the month"
the date in the month, 1..31, of the nth weekday
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Determine the date in the month, 1..31, of the nth weekday.