human
backlog backlog increased in 2015 compared to 2014 primarily due to higher orders on f-35 and c-130 programs. backlog decreased slightly in 2014 compared to 2013 primarily due to lower orders on f-16 and f-22 programs. trends we expect aeronautics 2019 2016 net sales to increase in the mid-single digit percentage range as compared to 2015 due to increased volume on the f-35 and c-130 programs, partially offset by decreased volume on the f-16 program. operating profit is also expected to increase in the low single-digit percentage range, driven by increased volume on the f-35 program offset by contract mix that results in a slight decrease in operating margins between years. information systems & global solutions our is&gs business segment provides advanced technology systems and expertise, integrated information technology solutions and management services across a broad spectrum of applications for civil, defense, intelligence and other government customers. is&gs 2019 technical services business provides a comprehensive portfolio of technical and sustainment services. is&gs has a portfolio of many smaller contracts as compared to our other business segments. is&gs has been impacted by the continued downturn in certain federal agencies 2019 information technology budgets and increased re-competition on existing contracts coupled with the fragmentation of large contracts into multiple smaller contracts that are awarded primarily on the basis of price. is&gs 2019 operating results included the following (in millions):.
|  | 2015 | 2014 | 2013 |
| --------- | --------- | --------- | --------- |
| Net sales | $5,596 | $5,654 | $6,115 |
| Operating profit | 508 | 472 | 498 |
| Operating margins | 9.1% | 8.3% | 8.1% |
| Backlog at year-end | $4,800 | $6,000 | $6,300 |
2015 compared to 2014 is&gs 2019 net sales decreased $58 million, or 1% (1%), in 2015 as compared to 2014. the decrease was attributable to lower net sales of approximately $395 million as a result of key program completions, lower customer funding levels and increased competition, coupled with the fragmentation of existing large contracts into multiple smaller contracts that are awarded primarily on the basis of price when re-competed (including cms-citic). these decreases were partially offset by higher net sales of approximately $230 million for businesses acquired in 2014; and approximately $110 million due to the start-up of new programs and growth in recently awarded programs. is&gs 2019 operating profit increased $36 million, or 8% (8%), in 2015 as compared to 2014. the increase was attributable to improved program performance and risk retirements, offset by decreased operating profit resulting from the activities mentioned above for net sales. adjustments not related to volume, including net profit booking rate adjustments and other matters, were approximately $70 million higher in 2015 compared to 2014. 2014 compared to 2013 is&gs 2019 net sales decreased $461 million, or 8% (8%), in 2014 as compared to 2013. the decrease was primarily attributable to lower net sales of about $475 million due to the wind-down or completion of certain programs, driven by reductions in direct warfighter support (including jieddo); and approximately $320 million due to decreased volume in technical services programs reflecting market pressures. the decreases were offset by higher net sales of about $330 million due to the start-up of new programs, growth in recently awarded programs and integration of recently acquired companies. is&gs 2019 operating profit decreased $26 million, or 5% (5%), in 2014 as compared to 2013. the decrease was primarily attributable to the activities mentioned above for sales, partially offset by severance recoveries related to the restructuring announced in november 2013 of approximately $20 million in 2014. adjustments not related to volume, including net profit booking rate adjustments, were comparable in 2014 and 2013. .
Please answer the following questions with expressions if necessary.
what was the backlog at year-end in 2015?
assistant
4800
human
and what was it in 2014?
assistant
6000
human
what was, then, the total backlog at year-end for the two years?
assistant
add(4800, 6000)
human
including 2013, what then becomes that total for the three years?
assistant
add(4800, 6000), add(#0, 6300)
human
and what is the backlog at year-end between those three years?
assistant
add(4800, 6000), add(#0, 6300), divide(#1, const_3)