I can't make out what's in series and what's in parallel in this circuit.
The solution I've thought of so far is to consider R1 in series with R4 and R2 in series with R5. Then, (R1+R4), R3 and (R2+R5) would be in parallel and their resultant resistance would be in parallel with R6. I'm not entirely certain this solution is correct though.
A nudge in the right direction would be appreciated.