Task: Question Understanding
Input (English): Passage: With the end of the "crack epidemic" in the mid-1990s and with the initiation of aggressive policing under mayors David Dinkins and subsequently  Rudolph Giuliani, crime in Harlem plummeted. In 1981, 6,500 robberies were reported in Harlem; robberies dropped to 4,800 in 1990 during David Dinkins mayoralty. By 2000, only 1,700 robberies were reported, and by 2010, only 1,100 were reported. There have been similar changes in all categories of crimes tracked by the New York City Police Department. In the 32nd Precinct, which services Central Harlem above 127th Street, for example, between 1990 and 2013, the murder rate dropped 89.4%, the rape rate dropped 67.5%, the robbery rate dropped 74.2%, burglary dropped 93.4%, and the total number of crime complaints dropped 77.6%.
Question: How many mayors were there during this time?
Output (English): number