  We obtain and analyze the phase diagram of doped iron-pnictides under the
assumption that doping adds non-magnetic impurities to the system but does not
change the densities of carriers. We show that the phase diagram is quite
similar to the one obtained under the opposite rigid band assumption. In both
cases, there is a phase where extended s+- superconductivity and
antiferromagnetism co-exist. We evaluate the jump of the specific heat at the
superconducting transition across the phase diagram and show that the jump is
non-monotonic, with the maximum at the onset of the co-existence phase. Our
results are in quantitative agreement with experiments on some iron-pnictides.
