In a class of 200 students, 125 students have taken Programming Language course, 85 students have taken Data Structure course, 65 students have taken Computer Organization course; 50 students have taken both Programming Language and Data Structures, 35 students have taken both Data Structures and Computer Organization; 30 students have taken both Data Structures and Computer Organization, 15 students have taken all the three course.
How many students have not taken any of the three courses?