This 365-day calendar corresponded was divided into 18 'months' of 20 days each, plus 5 'nameless' days at the end of the year. The 365 day year had no leap year so it varied from the solar year by a quarter of a day each year. The years were given their name in much the same way as the days of the 260-day calendar, 20 names were paired with 13 numbers giving 52 different possibilities for year names. How many days of the 365-day calendar were not included in months?