Find pth percentile of a stream of numbers

Question

I want to find the pth percentile of a stream of integers, exactly (not approximately).

If we know the number of integers which will be coming in the stream and the numbers can fit into the memory then we can simply sort the integers and find the pth percentile.

But, what if all the numbers can't be fit in memory? How can we do that?

We can assume all integers are 64-bit integers.