Two towns are connected only by a daily bus and a daily train, each of which goes through a valley. On any given day, one or more of the following mutually independent events may happen:

the bus breaks down with probability3/17.

the train break down with probability4/17.

a storm closes down the valley to both the bus and train with probability1/17.

What is the probability that travel between the two towns is possible tomorrow? Probability =