From "The Wages of Destruction: The Making and Breaking of the Nazi Economy":

The Germans introduced a new currency called the Rentenmark. The older Marks were redeemed into the Rentenmark at one trillion old marks to one Rentenmark.

The Rentenmark was replaced by Reichsmark in 1924 at a 1-1 ratio. The Reichsmark traded at 4.2 RM to the dollar.