  Primary proton spectrum in the energy range $5-10^3$ TeV is reconstructed
from the sea level muon spectrum with the use of QGSJET01 and SYBILL2.1
interaction models. Heavier nuclei are taken in accordance with the direct
measurements data, 100% uncertainty in helium flux is accounted for. The
obtained proton intensity strongly contradicts to the available data of balloon
experiments, exceeding them at the least by 100% for QGSJET01. This discrepancy
is due to the combined effect of primary nucleon flux underestimation in the
direct measurements and incorrect description of extensive air shower
development. In the latter case it is required earlier shower development and
harder spectra of secondary pions and kaons in comparison with QGSJET01. This
conclusion is in agreement with the obtained by the KASCADE group on the basis
of events rate study.
