HackerRank MySQL - Weather Observation Station 4

Let N be the number of CITY entries in STATION, and let N^ be the number of distinct CITY names in STATION; query the value of N-N^ from STATION. In other words, find the difference between the total number of CITY entries in the table and the number of distinct CITY entries in the table.

SELECT COUNT(CITY) - COUNT(DISTINCT CITY)
FROM STATION;