  We study the nonlinear stage of the modulation instability of a condensate in
the framework of the focusing Nonlinear Schr\"{o}dinger Equation. We find a
general N-solitonic solution of the focusing NLSE in the presence of a
condensate by using the dressing method. We separate a special designated class
of "regular solitonic solutions" that do not disturb phases of the condensate
at infinity by coordinate. All regular solitonic solutions can be treated as
localized perturbations of the condensate. We find an important class of
"superregular solitonic solutions" which are small perturbations at certain a
moment of time. They describe the nonlinear stage of the modulation instability
of the condensate.
