Grouping and aggregating data in pandas

We have a DataFrame which contains the date, the island name, and a count of how many times a certain penguin-like creature was seen on that particular date on the island. Here is the head sample:

        date  island  count
0 2022-09-01    Java     12
1 2022-09-02  Taiwan      1
2 2022-09-03  Taiwan     34
3 2022-09-04   Luzon     33
4 2022-09-05   Luzon      7

Select the line that will return the count of the unique islands. Suppose we did not write or import any additional functions.