{"pre_text": ["devon energy corporation and subsidiaries notes to consolidated financial statements 2013 ( continued ) restricted stock awards and units restricted stock awards and units are subject to the terms , conditions , restrictions and limitations , if any , that the compensation committee deems appropriate , including restrictions on continued employment .", "generally , the service requirement for vesting ranges from zero to four years .", "during the vesting period , recipients of restricted stock awards receive dividends that are not subject to restrictions or other limitations .", "devon estimates the fair values of restricted stock awards and units as the closing price of devon 2019s common stock on the grant date of the award or unit , which is expensed over the applicable vesting period .", "performance-based restricted stock awards performance-based restricted stock awards are granted to certain members of devon 2019s senior management .", "vesting of the awards is dependent on devon meeting certain internal performance targets and the recipient meeting certain service requirements .", "generally , the service requirement for vesting ranges from zero to four years .", "in order for awards to vest , the performance target must be met in the first year , and if met , recipients are entitled to dividends on the awards over the remaining service vesting period .", "if the performance target and service period requirements are not met , the award does not vest .", "devon estimates the fair values of the awards as the closing price of devon 2019s common stock on the grant date of the award , which is expensed over the applicable vesting period .", "performance share units performance share units are granted to certain members of devon 2019s senior management .", "each unit that vests entitles the recipient to one share of devon common stock .", "the vesting of these units is based on comparing devon 2019s tsr to the tsr of a predetermined group of fourteen peer companies over the specified two- or three- year performance period .", "the vesting of units may be between zero and 200% ( 200 % ) of the units granted depending on devon 2019s tsr as compared to the peer group on the vesting date .", "at the end of the vesting period , recipients receive dividend equivalents with respect to the number of units vested .", "the fair value of each performance share unit is estimated as of the date of grant using a monte carlo simulation with the following assumptions used for all grants made under the plan : ( i ) a risk-free interest rate based on u.s .", "treasury rates as of the grant date ; ( ii ) a volatility assumption based on the historical realized price volatility of devon and the designated peer group ; and ( iii ) an estimated ranking of devon among the designated peer group .", "the fair value of the unit on the date of grant is expensed over the applicable vesting period .", "the following table presents the assumptions related to performance share units granted. ."], "post_text": ["stock options in accordance with devon 2019s incentive plans , the exercise price of stock options granted may not be less than the market value of the stock at the date of grant .", "in addition , options granted are exercisable during a period established for each grant , which may not exceed eight years from the date of grant .", "the recipient must pay the exercise price in cash or in common stock , or a combination thereof , at the time that the option is exercised .", "generally , the service requirement for vesting ranges from zero to four years .", "the fair value of stock options on ."], "table": [["", "2015", "2014", "2013"], ["grant-date fair value", "$ 81.99 2013 $ 85.05", "$ 70.18 2013 $ 81.05", "$ 61.27 2013 $ 63.48"], ["risk-free interest rate", "1.06% ( 1.06 % )", "0.54% ( 0.54 % )", "0.26% ( 0.26 % ) 2013 0.36% ( 0.36 % )"], ["volatility factor", "26.2% ( 26.2 % )", "28.8% ( 28.8 % )", "30.3% ( 30.3 % )"], ["contractual term ( years )", "2.89", "2.89", "3.0"]], "table_ori": [["", "2015", "2014", "2013"], ["Grant-date fair value", "$81.99 – $85.05", "$70.18 – $81.05", "$61.27 – $63.48"], ["Risk-free interest rate", "1.06%", "0.54%", "0.26% – 0.36%"], ["Volatility factor", "26.2%", "28.8%", "30.3%"], ["Contractual term (years)", "2.89", "2.89", "3.0"]]}

Question: in years , what is the average contractual term for 2013 , 2014 , 2015?
Evidence:
table_4: the contractual term ( years ) of 2015 is 2.89 ; the contractual term ( years ) of 2014 is 2.89 ; the contractual term ( years ) of 2013 is 3.0 ;
text_18: the following table presents the assumptions related to performance share units granted. .
Program: add(2.89, 2.89), add(#0, const_3), divide(#1, const_3)
Answer:
str_answer: 2.9266
exe_answer: 2.92667