performance share awards the vesting of psas is contingent upon meeting various individual , divisional or company-wide performance conditions , including revenue generation or growth in revenue , pretax income or earnings per share over a one- to five-year period .the performance conditions are not considered in the determination of the grant date fair value for these awards .the fair value of psas is based upon the market price of the aon common stock at the date of grant .compensation expense is recognized over the performance period , and in certain cases an additional vesting period , based on management 2019s estimate of the number of units expected to vest .compensation expense is adjusted to reflect the actual number of shares issued at the end of the programs .the actual issuance of shares may range from 0-200% ( 0-200 % ) of the target number of psas granted , based on the plan .dividend equivalents are not paid on psas .information regarding psas granted during the years ended december 31 , 2011 , 2010 and 2009 follows ( shares in thousands , dollars in millions , except fair value ) : .
[['', '2011', '2010', '2009'], ['target psus granted', '1715', '1390', '3754'], ['fair value ( 1 )', '$ 50', '$ 39', '$ 38'], ['number of shares that would be issued based on current performance levels', '1772', '1397', '2300'], ['unamortized expense based on current performance levels', '$ 60', '$ 18', '$ 4']]
( 1 ) represents per share weighted average fair value of award at date of grant .during 2011 , the company issued approximately 1.2 million shares in connection with the 2008 leadership performance plan ( 2018 2018lpp 2019 2019 ) cycle and 0.3 million shares related to a 2006 performance plan .during 2010 , the company issued approximately 1.6 million shares in connection with the completion of the 2007 lpp cycle and 84000 shares related to other performance plans .stock options options to purchase common stock are granted to certain employees at fair value on the date of grant .commencing in 2010 , the company ceased granting new stock options with the exception of historical contractual commitments .generally , employees are required to complete two continuous years of service before the options begin to vest in increments until the completion of a 4-year period of continuous employment , although a number of options were granted that require five continuous years of service before the options are fully vested .options issued under the lpp program vest ratable over 3 years with a six year term .the maximum contractual term on stock options is generally ten years from the date of grant .aon uses a lattice-binomial option-pricing model to value stock options .lattice-based option valuation models use a range of assumptions over the expected term of the options .expected volatilities are based on the average of the historical volatility of aon 2019s stock price and the implied volatility of traded options and aon 2019s stock .the valuation model stratifies employees between those receiving lpp options , special stock plan ( 2018 2018ssp 2019 2019 ) options , and all other option grants .the company believes that this stratification better represents prospective stock option exercise patterns .the expected dividend yield assumption is based on the company 2019s historical and expected future dividend rate .the risk-free rate for periods within the contractual life of the option is based on the u.s .treasury yield curve in effect at the time of grant .the expected life of employee stock options represents the weighted-average period stock options are expected to remain outstanding and is a derived output of the lattice-binomial model. .

Question: what is the lowest value of unamortized expense during this period?
Answer: 4
Explanation: it is the minimum value of unamortized expense .