1998 Toyota Camry frozen condensation in exhaust system

I live in a cold climate and my car stood outdoors for almost a week, with an automatic ignition system kicking in about 10 times per day to keep the engine warm. However, a lot of condensation seems to have frozen in the exhaust system. Now the engine won't climb over 20 mph, and very little exhaust comes out the tailpipe -- mostly steam escapes from behind the engine block.

What is the best way to clean out the exhaust system of this frozen condensation?

Thank you,

Michael