MathDB

Japanese businessman Rui lives in America and makes a living from trading cows. On Black Thursday he was selling his cows for

2000

dollars each (the cows were of the same price), but after the financial crash there were huge fluctuations in the market and Rui was forced to follow them with his pricing. Every day he doubled, halved, multiplied by five or divided by five the price from the previous day (even if it meant he had to give change in cents). At the same time he managed to follow the Japanese superstition, so that the integer part of the price in dollars never started with digit

4

. On the day when Billy visited him to buy some cows the price of each cow was

80

dollars. What is the minimal number of days that could have passed since Black Thursday by then?

Problem Statement