For the three events A, B, and C, P (exactly one of the events A or B occurs) = P (exactly one of the two events B or C occurs) = P(exactly one of the events C or A occurs) = $p$ and P (all the three events occur simultaneously) = $p^2$, where $0 < p < \frac{1}{2}$. Then the probability of at least one of the three events A, B and C occuring is