Non-parallel, non-sequential circuit
The trick here is to simplify.

Starting from the furthest point away from the power source, combine the resistors in pairs and replace those pairs with a single resistor.  Keep going until you have only one resistor.

\$R_3\$ and \$R_6\$ add together to form a single resistor.  That new resistor (we'll call it \$R_{36}\$) is then in parallel with \$R_5\$. Combine those to make a new resistor \$R_{536}\$.  Keep going like that until you have just one resistor left.

That resistor is known as the "Thevenin equivalent resistance".