The system of equations \begin{eqnarray*}\log_{10}(2000xy) - (\log_{10}x)(\log_{10}y) & = & 4 \\ \log_{10}(2yz) - (\log_{10}y)(\log_{10}z) & = & 1 \\ \log_{10}(zx) - (\log_{10}z)(\log_{10}x) & = & 0 \\ \end{eqnarray*} has two solutions $$(x_{1},y_{1},z_{1})$$ and $$(x_{2},y_{2},z_{2})$$. Find $$y_{1} + y_{2}$$.

(第十八届AIME1 2000 第9题)