Mr. Li spent 3,000 yuan to buy a stock in 2011, which can increase in value by an average of 50% per year. If Mr. Li has been holding such stocks, the total value of these stocks will exceed 30,000 yuan after at least how many years.
李先生2011年花3000元购得一种股票，这种股票平均每年可增值50%．如果李先生一直持有这种股票，至少经过多少年这些股票的总价值会超过30000元．
<result>6</result>