$R = A \times B + C$, How retrieve A and C if C is negative? For A = 18,  B = 54 and $C = {-53, 53}$

$$R = A \times B + C$$

I can retrieve A and C from R with:
$$
A = \lfloor R \div B \rfloor
$$
$$
C={R} \pmod {B}
$$
example, A = 18, C = 53:
$$
R = 18 \times 54 + 53
$$
found A and C:
$$
A = \lfloor {1025} \div {54} \rfloor = {18}
$$
$$
C = {1025} \pmod {54} = {53}
$$
But if C is negative the result if false, A = 18, C = -53:
$$
R= 18 \times 54 - 53
$$
$$
A = \lfloor {919} \div {54} \rfloor = {17}
$$
$$
C = {919} \pmod {54} = {1}
$$
How can I retrive A =18 and C = -53 ?
$$A=\left\lceil 919/54\right\rceil =18$$
For, C$$1\equiv1-54\equiv -53(\mod 54)$$
$$A=\left\lceil 919/54\right\rceil =18$$
For, C$$1\equiv1-54\equiv -53(\mod 54)$$