Heat And Thermodynamics

Consider two Carnot engines of efficiencies $\eta_1$ and $\eta_2$. The first engine absorbs heat $Q_1$ from a heat reservoir $A$ and releases heat $Q_2$ to a heat reservoir $B$. The second engine takes heat $Q_2$ from $B$ and releases heat $Q_3$ to a heat reservoir $C$. If $Q_1 > Q_2 > Q_3$, what is the net efficiency of this combination of the two Carnot engines?