Suppose that an absentmined secretary wrote n letters and sealed them in envelops before writing the addresses on the envelops. Then she wrote the n addresses on the envelops at random. What is the prob that at least one letter was addressed correctly?

Im thinking to find the prob that no one was addressed right then subtract it from 1, and the chance address the first one right is 1/5, and the second one is 1/4, what if the first one was wrong already?