A substance, the internal energy of which $U$ is related to pressure $P$ and volume $V$ by the relation $U = k P V$, performs a thermodynamic cycle consisting of an isobaric, isochoric and adiabatic processes. The work done by the substance during the isobaric process is $m = 5$ times greater than the work of external forces to compress the substance during the adiabatic process. The efficiency of the cycle is $\eta = 1/4$.