At least 5 interviews in their office or via Skype.

Each interview is one hour long with a different interviewer.

One of the interviews can be about the architecture of distributed high-load systems and load balancing.

The problems are essentially the same and not very difficult. An interviewer will give hints and allow you to correct your bugs. However, if you don't understand or follow the hint, you will likely fail that problem and be rejected.

Medium difficulty.

No dynamic programming, no templates, no class hierarchy, no Unix shell or command line tools, no mutex, no lock-free structures.

Some questions are about processing a stream of data; others are not. You should find a way to combine basic data structures. You must achieve the required O() complexity.