On August 1, a group of students are standing in rows, with 12 students in each row. On August 2, the same group is standing with all of the students in one long row. This process continues through August 14 with a different number of students per row each day. However, on August 15, they cannot find a new way of organizing the students. What is the smallest possible number of students in the group?
144
168
192
216
240