$\frac{1}{1 \times 2 \times 3} + \frac{1}{2 \times 3 \times 4} + \frac{1}{3 \times 4 \times 5} + ... +\frac{1}{98 \times 99 \times 100}$.

The expression above can be expressed in a form of $\dfrac{1}{p} - \dfrac{1}{q}$, where $p$ and $q$ are positive integers. Find the value of $p+q$.