Table:
|  | December 31, 2019 | December 31, 2018 | December 31, 2017 |
| --- | --- | --- | --- |
| Cost of sales | 22 | 23 | 12 |
| Selling, general and administrative | 46 | 67 | 31 |
| Research and development | 77 | 35 | 18 |
| Total pre-payroll tax and social contribution compensation | 145 | 125 | 61 |
Paragraphs:
The following table illustrates the classification of pre-payroll tax and social contribution stock-based compensation expense included in the consolidated statements of income for the years ended December 31, 2019, December 31, 2018 and December 31, 2017:
The fair value of the shares vested in 2019 was $114 million compared to $68 million for 2018 and $38 million for 2017.
Compensation cost, excluding payroll tax and social contribution, capitalized as part of inventory was $6 million as of December 31, 2019, compared to $6 million as of December 31, 2018 and $3 million as of December 31, 2017. As of December 31, 2019, there was $138 million of total unrecognized compensation cost related to the grant of unvested shares, which is expected to be recognized over a weighted average period of approximately 9 months.
The total deferred income tax benefit recognized in the consolidated statements of income related to unvested share-based compensation expense amounted to $9 million, $7 million and $3 million for the years ended December 31, 2019, 2018 and 2017, respectively.
Question:
What was the increase ./ (decrease) in the cost of sales from 2018 to 2019?
Answer: 22 - 23 = -1