Well, since I was already pretty tired, at the begining I started writing something wrong. Then one of the interviewers said, wait, see that you must return three digits exactly after the point, and I said, yes, it means that the result of SQRT should be multiplied by 1000, that is its input should be multiplied by 1M. Then I wrote: float SQRT2(int x){ return (SQRT(x*1000000)/1000.0); } Then, one of them explained me why I am right, I even didn't have strengths to say to her that somehow if I wrote it by myself, I do understand it.:) Finally, she said to me good luck and I felt that it means "Go to..., I are definitely bad personality":) Well, next time I will be much nicer person:) Good luck to us all !:)