Anomalous dimension of the simplest nontrivial single impurity operator in
the beta=1/2 deformed theory is determined at six loops from the AdS/CFT
correspondence. L\"uscher correction is evaluated at next-to-next-to-leading
order (NNLO) in terms of multiple zeta values. The result can be simplified
into the products of simple zeta functions and the same form of the correction
is expected for the Konishi operator at six loops, too.Comment: 14 pages, references added, numeric coefficient in (5) corrected,
which changes the numerical result, but not its structur