A doctor sees 10 patients in one day. The following is a list of their ailments. Patient 1 - seasonal allergies Patient 2 - common cold Patient 3 - sinus infection Patient 4 - seasonal allergies Patient 5 - chronic heartburn Patient 6 - seasonal allergies Patient 7 - migraines Patient 8 - back pain Patient 9 - broken wrist Patient 10 - chronic heartburn Which of the ailments listed had a frequency of three?