private int _dashTiles;
private Vector3 _direction;

void Update(){
	if (_dashTiles > 0) {
		characterController.Move(_direction);
		_dashTiles--;
	}
}

private void Movement() {
	...
	if (Input.GetKey(KeyCode.LeftShift) && _dashTiles == 0) {

		_dashTiles = 5;
		_direction = Vector3.right;
	}
}