  We study the heavy-heavy-light (HHL) three-point functions in the planar N =
4 super-Yang- Mills theory using the recently proposed hexagon bootstrap
program [arXiv:1505.06745]. We prove the conjecture of Bajnok, Janik and
Wereszczynski [arXiv:1404.4556] on the polynomial L-dependence of HHL structure
constant up to the leading finite-size corrections, where L is the length of
the heavy operators. The proof is presented for a specific set-up but the
method can be applied to more general situations.
