Counting Student Preferences for Extracurricular Activities

In a recent survey conducted among 200 high school students, the preferences for extracurricular activities were recorded. The results indicated that 80 students preferred sports, 60 preferred music, and 40 preferred art. Additionally, 20 students expressed interest in both sports and music, 15 in both music and art, and 5 in both sports and art. If we denote the set of students preferring sports as $S$, music as $M$, and art as $A$, how many students preferred only one type of activity? Calculate the number of students in the set defined by the count of those who liked exactly one activity.