Alex80 wrote you a translated address, however it is written for Russian postmen, so I advice you to address your card that way:

Rudic Sergey
ul. Shevchenko, 3A/58
Sovetsk
Kaliningradskaya Oblast
RUSSIA (РОССИЯ)
238700

It would be the most fitable format.
However, you can still use Alex80's format and it will be sent.

Also you can ask in your postcard if they know where Sergey lives. New inhabitants can know it, if he does not live there anymore. It is better to write that part in Russian.