Every student in my school is in either French class or Spanish class, or both. Let be the number of students in French class,&nb

Every student in my school is in either French class or Spanish class, or both. Let  be the number of students in French class,  be the number of students in Spanish class, and  be the number of students who are in both classes. Find an expression in terms of , , and  for how many students there are in my school.