  Inverse spectral problem for a self-adjoint differential operator, which is
the sum of the operator of the third derivative on a finite interval and of the
operator of multiplication by a real function (potential), is solved. Closed
system of integral linear equations is obtained. Via solution to this system,
the potential is calculated. It is shown that the main parameters of the
obtained system of equations are expressed via spectral data of the initial
operator. It is established that the potential is unambiguously defined by the
four spectra.
