# End of the world

**Calculus**Level 5

\[\large \displaystyle \sum^{\infty}_{a=0} \displaystyle \sum^{\infty}_{b=0} \displaystyle \sum^{\infty}_{c=0}\dfrac{a+b+c+abc} {2^a(2^{a+b}+2^{b+c}+2^{a+c})}\]

If the value of above expression is the form of \( \dfrac ab\), where \(a\) and \(b\) are coprime positive integers, find \(a+b\).