Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
|  | Year Ended December 31, | Year Ended December 31, | Year Ended December 31, | Year Ended December 31, | Year Ended December 31, |
| --- | --- | --- | --- | --- | --- |
|  | 2018 | 2017 | 2016 | 2015 | 2014 |
| Revenue passenger miles (in millions) | 225,243 | 217,712 | 213,098 | 209,625 | 202,925 |
| Available seat miles (in millions) | 263,365 | 254,325 | 251,867 | 246,764 | 239,676 |
| Passenger mile yield | 17.65¢ | 16.97¢ | 16.81¢ | 16.59¢ | 17.22¢ |
| Passenger revenue per available seat mile | 15.09¢ | 14.53¢ | 14.22¢ | 14.10¢ | 14.58¢ |
| Total revenue per available seat mile | 16.87¢ | 16.18¢ | 15.66¢ | 16.50¢ | 16.84¢ |
| Operating cost per available seat mile | 14.87¢ | 13.83¢ | 12.89¢ | 13.33¢ | 15.92¢ |
| Passenger load factor | 85.5% | 85.6% | 84.6% | 84.9% | 84.7% |
| Fuel gallons consumed (in millions) | 4,113 | 4,032 | 4,016 | 3,988 | 3,893 |
| Average price per fuel gallon (2) | $2.20 | $1.68 | $1.49 | $1.90 | $3.47 |
| Full-time equivalent employees, end of period | 88,680 | 86,564 | 83,756 | 82,949 | 79,655 |
Question:
How much fuel has been consumed by Delta Airlines in 2018?
Answer:
4,113