  We consider the Schr\"odinger operator in the plane with delta-potential
supported by a curve. For the cases of an infinite curve and a finite loop we
give estimates on the lower bound of the spectrum expressed explicitly through
the strength of the interaction and a parameter which characterizes geometry of
the curve. Going further we cut the curve into finite number of pieces and
estimate the bottom of the spectrum using the parameters for the pieces. As an
application of the elaborated theory we consider a curve with a finite number
of cusps and "leaky" quantum graphs.
