Original: In December 1923 the exchange rate was 4,200,000,000,000 Marks to 1 US dollar.Bresciani-Turroni, page 335 In 1923, the rate of inflation hit 3.25 × 106 percent per month (prices double every two days).
Simplified: In December of 1923 the exchange rate was 4,200,000,000,000 Marks to 1 US dollar.