How many days early could people purchase tickets to the opening ceremony if they registered online?
return people could purchase tickets to the  opening ceremony ;return days of #1 ;return #2 if they registered online ;return #2 besides  #3 ;return the  lowest of #4 ;return the  difference of #3 and  #5
['select', 'project', 'filter', 'discard', 'aggregate', 'arithmetic']