  Shashlyk-type electromagnetic calorimeter (ECal) of the Multi-Purpose
Detector at heavy-ion NICA collider is optimized to provide precise spatial and
energy measurements for photons and electrons in the energy range from about 40
MeV to 2-3 GeV. To deal with high multiplicity of secondary particles from
Au-Au reactions, ECal has a fine segmentation and consists of 38,400 cells
("towers"). Given the big number of "towers" and the time constraint, it is not
possible to calibrate every ECal "tower" with beam. In this paper, we describe
the strategy of the first-order calibration of ECal with cosmic muons.
