def is_leap_year(year): return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0) def days_in_month(year, month): if month == 2: return 29 if is_leap_year(year) else 28 elif month in [1, 3, 5, 7, 8, 10, 12]: return 31 else: return 30 def day_of_year(year, month, day): days = 0 for m in range(1, ...