Can anyone help me to solve this problem:

Consider $\displaystyle n$ as a natural number greater than $\displaystyle 1$. Prove that sum of all numbers of the form $\displaystyle \frac{1}{pq}$ with the condition $\displaystyle (p,q) = 1$ ($\displaystyle p$ and $\displaystyle q$ are relatively prime) and $\displaystyle 1 \leq p < q \leq n$ and $\displaystyle p + q > n$ is always equal to $\displaystyle \frac {1}{2}$