NEW YORK — The mayor’s office is reassuring the public that even if the blizzard that is expected to arrive late Monday leaves more than the predicted three feet of snow, there is no need to worry, as the city is preemptively dumping six trillion tons of salt on the streets. Mayor Bill de Blasio is asking residents to stay indoors during the storm, urging them to avoid getting caught in the salt mountains that city vehicles are busy piling all over the five boroughs. “In the great storms of 2010 and 2006, we barely had enough salt to dust the streets and sidewalks, which led to thousands of innocent New Yorkers suffering from violent slips, often causing them to comically dive head first into huge fluffy snow mounds,” de Blasio said. “But this year we’re totally prepared, and with any luck the snow will turn to slush even before it hits the ground.” If the salt mountains prove too large for the snow, de Blasio said he’s considering ordering the fire department to douse them with water as soon as the temperature rises above freezing.