There were 3 interviews in a row. First was about understanding algorithms and complexity theory. It was tough but really exiting. The interviewer was very friendly and encouraged me to think creatively which helped a lot. Second interview was about optimization solution design case. It was my pleasure to talk to an expert. The atmosphere was also really positive and stimulated creativity. Finally, I talked with the head of a department and he was so kind and honest to describe in details the company structure and a candidate's expected responsibilities.