On 1 April 2007, the parallel market was asking ZWD 30,000 for $1 USD. By year end, it was down to about ZWD 2,000,000. On 18 January 2008, the Reserve Bank of Zimbabwe began to issue higher denomination ZWD bearer cheques (a banknote with an expiry date), including $10 million bearer cheques - each of which was worth less than US $1.35 (70p Sterling; 0.90 Euro) on the parallel market at the time of first issue. On 4 April 2008 the Reserve Bank of Zimbabwe introduced new $25 million and $50 million bearer cheques. At the time of first issue they were worth US$0.70 & US$1.40 on the parallel market respectively.. How many months did it take for the ZWD to drop to 2,000,000 after April 2007?