Of the 195 grade-12 students at Vennville High School, 160 have signed up for biology, 121 for chemistry, and 126 for physics. The science students include 95 who are taking both biology and chemistry, 93 who are taking chemistry and physics, and 100 who are taking biology and physics, and 71 who are taking all 3 science courses. How many students are not taking any of these three science courses?