In Russian, only a few words are spelled with 'цы' instead of 'ци'
They can be memorized using a single phrase.
In Russian, "и" is written after "ц" in the root of a word: "цифра" (digit), "цирк" (circus) and "медицина" (medicine). However, there are exceptions that must simply be memorized. A helpful phrase is: "цыган встал на цыпочки и сказал цыпленку “цыц”." (The gypsy stood on tiptoes and said "tsk tsk" to the chick.)
However, if the syllable "цы" comes at the end of a word, it is spelled with "ы": for example, "птицы" (birds) or "леденцы" (lollipops).