Suppose there are three threads A$,$ B and C$.$ A has two sequential sections of code a$1$

and a$2,$ B has two sequential sections of code b$1$ and b$2,$ C has $1$ section of code c$1.$

The execution of c$1$ in threads C needs to wait the completion of a$1$ and b$1$ in thread A and B

respectively; The execution of a$2$ needs to wait for the completion of b$2.$ Use semaphores to

solve the synchronization problem. You need to define and initialize the semaphores.