Service by a cascaded network of instruments

The service system under consideration consists of $n$ instruments. The first of these receives a stationary ordinary ergodic flux of entries. The entry serviced by the $k$-th instrument, $k=\overline{1, n-1}$ is recieved by the $k+1$-st instrument of this is free and lost if otherwise. The servicing time in each instrument has an exponential distribution. A formula for the probability of losses is given.