Consider the expression $(a-1)*\left(\dfrac{(b+c)}{3}+d\right)$.

Let $x$ be the minimum number of registers required by an optimal code generation (without any register spill) algorithm for a load/store architecture in which

(i) Only load and store instructions can have memory operands and

(ii) Arithmetic instructions can have only register or immediate operands.

The value of $x$ is _______.