"S-300 itself will be a target for unmanned weapons, cruise missiles, etc." - Pedro First you have to know where it is. Then you have to hit it. The entire system is mobile, and capable of being ready in about 15 minutes from halting movement. The S-300PMU1 system has a Pk of .7 against tactical ballistic missiles and higher against cruise missiles. The S-300PM1 would significantly complicate any strike against Iran.
EU's Tusk warns Turkey to cut refugee flow (Reuters)
from the article: Russia to supply Iran with S-300 defense systems