We studied spectra of two flares very similar by power in the optical region, but very different by spectral features and the total energy. One of them is an unique flare of 28 October 2003, its importance is X17.2/4B, it is the third in size amongst the registered flares. The second flare took place on 1 September 1990, its importance is 3B. The flares are distinguished by the value of Balmer decrement. For the flare of 28 October 2003 the ratio I(H_β)/I(H_α) = 1.47. This is the maximum value that was observed for solar flares. The flares are also different with regard to the intensity of the D Na I lines: the emission of these lines is much bigger for the flare of 28 October 2003. The model chromospheres of these flares are calculated by the use of the observed profiles of Balmer lines and D Na I lines. The simultaneous interpretation of all observed profiles proved to be impossible. Much more better agreement between calculated and observed profiles was obtained with two-component model in which the hot component occupies 6 % of the area. Hot components of the models are characterized by the presence of thick condensations in the upper layers. This condensation is situated on greater depth and contains more substance for the flare of 28 October 2003 as compared with the second flare. The intensity of H_α line in the hot component separately is about 30 and the continuum intensity is 3 % of the undisturbed intensity. For the flare of 28 October 2003 the model photosphere is also calculated using the observed profiles of photospheric lines. It was concluded that very broad profiles of sigma-components of the line of Fe I λ 525.0 nm could be explained only by the suggestion that the magnetic field in the photospheric layers of the flare is very inhomogeneous — the magnetic fields of different directions are present. We obtained a large difference between the values of magnetic field obtained deduced by the separation of the sigma-components and by the simulation.