# Don't run out of patience

Algebra Level 5

$\large \sum _{r=1} ^n \dfrac{1}{r(r+1)(r+2)(r+3)}$

If the closed form of the partial sum above can be expressed as $\large \dfrac{1}{a} - \dfrac{1}{b(n+1)}+ \dfrac{1}{c(n+2)}- \dfrac{1}{d(n+3)} \; ,$

where $$a,b,c$$ and $$d$$ are constants, find $$a+b+c+d$$.

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