How many people live in areas that would be flooded if sea levels rise?

It depends, of course, on how far the sea level rises, but let's say that most coastal cities in developed countries would be severely affected (New York; Portsmouth, UK; London; Hamburg and hundreds of others), so that's hundreds of millions for a start. Then there's all those small island nations such as the Maldives that would totally disappear with only a few metres rise.