Black hole mass spectrum vs spectrum of Hawking radiation

We consider a massive self-gravitating shell as a model for collapsing body and a null self-gravitating shell as a model for quanta of Hawking radiation. It is shown that the mass-energy spectra for the body and the radiation do not match. The way out of this difficulty is to consider not only out-going radiation but also the ingoing one. It means that the structure of black hole is changing during its evaporation resulting in the Bekenstein-Mukhanov spectrum for large masses.