Using sql group by and having

I'm quite new to SQL and I am trying to answer the exercise 8 of SQL ZOO, but I am missing something. Could you please help me?

List the continents that have a total population of at least 100 million.

What I am trying is:

select continent
from world
group by continent 
having count(population) >= 100000000

Your error was to use COUNT instead of SUM.

Try the following:

select continent
from world
group by continent
having sum(population) >= 100000000