There are $n$ cars located along an infinitely long road, positioned from left to right. You are given a $0$ indexed string directions of length $n$, where directions[i] denotes the initial state of the car at index i:

• 'L' indicates that the car is moving left.

• 'R' indicates that the car is moving right.

• 'S' indicates that the car is stationary.

All moving cars travel at the same constant speed.

Collisions occur based on the following conditions:

• If a car moving right collides with a car moving left, the total number of collisions increases by $2$, and both cars come to a stop, becoming stationary.

• If a moving car collides with a stationary car, the total number of collisions increases by $1$, and the moving car comes to a stop, becoming stationary.

Once a car becomes stationary, it remains at that position on the road.

Return the total number of collisions that occur on the road.

Constraints:

• $1 \leq$ directions.length $\leq 10^5$

• directions[i] is either 'L', 'R', or 'S'.

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