what was the total aircraft fuel expense from 2016 to 2018 in millions
Important information:
table_1: year the 2018 of gallons is 4447 ; the 2018 of average priceper gallon is $ 2.23 ; the 2018 of aircraft fuelexpense is $ 9896 ; the 2018 of percent of totaloperating expenses is 23.6% ( 23.6 % ) ;
table_2: year the 2017 of gallons is 4352 ; the 2017 of average priceper gallon is 1.73 ; the 2017 of aircraft fuelexpense is 7510 ; the 2017 of percent of totaloperating expenses is 19.6% ( 19.6 % ) ;
table_3: year the 2016 of gallons is 4347 ; the 2016 of average priceper gallon is 1.42 ; the 2016 of aircraft fuelexpense is 6180 ; the 2016 of percent of totaloperating expenses is 17.6% ( 17.6 % ) ;
Reasoning Steps:
Step: add1-1(9896, 7510) = 17406
Step: add1-2(#0, 6180) = 23586
Program:
add(9896, 7510), add(#0, 6180)
Program (Nested):
add(add(9896, 7510), 6180)

Please answer the following financial question based on the context provided. Make sure to give the answer in raw number, not in percentage and without any units. If the question asks for percentage the value should be less than 1
Context:
the following table shows annual aircraft fuel consumption and costs , including taxes , for our mainline and regional operations for 2018 , 2017 and 2016 ( gallons and aircraft fuel expense in millions ) . year gallons average price per gallon aircraft fuel expense percent of total operating expenses .
Table
year | gallons | average priceper gallon | aircraft fuelexpense | percent of totaloperating expenses
2018 | 4447    | $ 2.23                  | $ 9896               | 23.6% ( 23.6 % )                  
2017 | 4352    | 1.73                    | 7510                 | 19.6% ( 19.6 % )                  
2016 | 4347    | 1.42                    | 6180                 | 17.6% ( 17.6 % )                  
as of december 31 , 2018 , we did not have any fuel hedging contracts outstanding to hedge our fuel consumption . as such , and assuming we do not enter into any future transactions to hedge our fuel consumption , we will continue to be fully exposed to fluctuations in fuel prices . our current policy is not to enter into transactions to hedge our fuel consumption , although we review that policy from time to time based on market conditions and other factors . fuel prices have fluctuated substantially over the past several years . we cannot predict the future availability , price volatility or cost of aircraft fuel . natural disasters ( including hurricanes or similar events in the u.s . southeast and on the gulf coast where a significant portion of domestic refining capacity is located ) , political disruptions or wars involving oil-producing countries , economic sanctions imposed against oil-producing countries or specific industry participants , changes in fuel-related governmental policy , the strength of the u.s . dollar against foreign currencies , changes in the cost to transport or store petroleum products , changes in access to petroleum product pipelines and terminals , speculation in the energy futures markets , changes in aircraft fuel production capacity , environmental concerns and other unpredictable events may result in fuel supply shortages , distribution challenges , additional fuel price volatility and cost increases in the future . see part i , item 1a . risk factors 2013 201cour business is very dependent on the price and availability of aircraft fuel . continued periods of high volatility in fuel costs , increased fuel prices or significant disruptions in the supply of aircraft fuel could have a significant negative impact on our operating results and liquidity . 201d seasonality and other factors due to the greater demand for air travel during the summer months , revenues in the airline industry in the second and third quarters of the year tend to be greater than revenues in the first and fourth quarters of the year . general economic conditions , fears of terrorism or war , fare initiatives , fluctuations in fuel prices , labor actions , weather , natural disasters , outbreaks of disease and other factors could impact this seasonal pattern . therefore , our quarterly results of operations are not necessarily indicative of operating results for the entire year , and historical operating results in a quarterly or annual period are not necessarily indicative of future operating results . domestic and global regulatory landscape general airlines are subject to extensive domestic and international regulatory requirements . domestically , the dot and the federal aviation administration ( faa ) exercise significant regulatory authority over air carriers . the dot , among other things , oversees domestic and international codeshare agreements , international route authorities , competition and consumer protection matters such as advertising , denied boarding compensation and baggage liability . the antitrust division of the department of justice ( doj ) , along with the dot in certain instances , have jurisdiction over airline antitrust matters. .
Question: 
what was the total aircraft fuel expense from 2016 to 2018 in millions
Important information:
table_1: year the 2018 of gallons is 4447 ; the 2018 of average priceper gallon is $ 2.23 ; the 2018 of aircraft fuelexpense is $ 9896 ; the 2018 of percent of totaloperating expenses is 23.6% ( 23.6 % ) ;
table_2: year the 2017 of gallons is 4352 ; the 2017 of average priceper gallon is 1.73 ; the 2017 of aircraft fuelexpense is 7510 ; the 2017 of percent of totaloperating expenses is 19.6% ( 19.6 % ) ;
table_3: year the 2016 of gallons is 4347 ; the 2016 of average priceper gallon is 1.42 ; the 2016 of aircraft fuelexpense is 6180 ; the 2016 of percent of totaloperating expenses is 17.6% ( 17.6 % ) ;
Reasoning Steps:
Step: add1-1(9896, 7510) = 17406
Step: add1-2(#0, 6180) = 23586
Program:
add(9896, 7510), add(#0, 6180)
Program (Nested):
add(add(9896, 7510), 6180)
