code: def replace_u_end_day(day, year, month):
      
      day = day.lstrip('-')
      year = int(year)
      month = int(month.lstrip('-'))
      if day == 'uu' or day == '3u':
          # Use the last day of the month for a given year/month.
          return str(calendar.monthrange(year, month)[1])
      if day == '0u' or day == '1u':
          return day.replace('u', '9')
      if day == '2u' or day == 'u9':
          if month != '02' or calendar.isleap(year):
              return '29'
          elif day == '2u':
              # It is Feburary and not a leap year.
              return '28'
          else:
              # It is February, not a leap year, day ends in 9.
              return '19'
      # 'u2' 'u3' 'u4' 'u5' 'u6' 'u7' 'u8'
      if 1 < int(day[1]) < 9:
          return day.replace('u', '2')
      # 'u0' 'u1'
      if day == 'u1':
          if calendar.monthrange(year, month)[1] == 31:
              # See if the month has a 31st.
              return '31'
          else:
              return '21'
      if day == 'u0':
          if calendar.monthrange(year, month)[1] >= 30:
              return '30'
      else:
          return '20'
docs: Find the latest legitimate day.