Robot on the Number Line

The robot starts at point $0$ on a numerical axis and executes a series of learned moves. The first move has a length of $1$, and each subsequent move is three times the length of the previous one. For each move, the robot can either stay in place (S) or move in a chosen direction: right (R) or left (L), by the length of the current move.

Given an integer $N$ (-10^{17} \leq N \leq 10^{17}), determine if the robot can reach a point on the axis with this coordinate. If it is possible, provide a sequence of moves. If there are multiple valid sequences, return any one that does not end with S, unless S is the only move. If the robot cannot reach the desired point, output Impossible.