Let $U=2\cdot 2004^{2005}$, $V=2004^{2005}$, $W=2003\cdot 2004^{2004}$, $X=2\cdot 2004^{2004}$, $Y=2004^{2004}$ and $Z=2004^{2003}$. Find the largest value among the expressions $U-V$, $V-W$, $W-X$, $X-Y$, and $Y-Z$. The expression $U-V$ can be written in the form $k\cdot 2004^{m}$. Please find the value of $k + m$.

Let's think step by step and output the final answer within \boxed{}.
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