As in America, I'm sure it's common for friends in Russia to tell each other good night in less formal terms. I'm almost sure I heard my friend say "ночь" one night as opposed to spokoinoi nochi or dobriy nochi. This would be like saying "night" as a less formal way of saying "good night". Is this correct and would it be said "ночь" or "ночи"? I'm a beginner.