"B. Pengö" means "Billion Pengö", but with a European "Billion", which would be a trillion Pengö in American counting. So the printed, but never circulated "1.000.000.000 B.-Pengő" bill was actually "worth" 10^21 Pengö.

When Hungary introduced the Forint in 1946, the exchange rate was 1 Forint = 400.000.000.000.000.000.000.000.000.000 Pengő.

That's at least what German Wikipedia says, no matter how incredible it may sound.