  A direct method for calculating the minimal length of ``one-dimensional''
Josephson junctions is proposed, in which the specific distribution of the
magnetic flux retains its stability. Since the length of the junctions is a
variable quantity, the corresponding nonlinear spectral problem as a problem
with free boundaries is interpreted. The obtained results give us warranty to
consider as ``long'', every Josephson junction in which there exists at least
one nontrivial stable distribution of the magnetic flux for fixed values of all
other parameters.
