what is id of students who registered some courses but the least number of courses in these students?
return students  ;return #1 who  registered courses  ;return courses  #2 registered ;return number of  #3 for each  #2 ;return #2 where #4 is  lowest ;return ids of  #5
['select', 'filter', 'project', 'group', 'superlative', 'project']