Did you know that the majority of Russian sunames end in -ин (-ын) or -ов (-ев), for masculine surnames, and -ина (-ына) or -ова (-ева) for feminine surnames? There is also a big group of Russian surnames that end in -ий (-ый) or -ая (-яя). The last group has the declension of a normal adjective.
The declension of the first group of surnames is special. Masculine nouns are declined as nouns, except for the Instrumental case. Feminine nouns are declined as adjectives, except for the Accusative case, when it has the form of a noun. Let’s take an example, Пушкин and Ахматова.
I. Пушкиным, exception, declined as an adjective, for example, красивый.
A. Ахматову, exception, declined as a noun, for example, чашку.