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:
| Locomotive | Named | Serial No | Entered service | Gauge | Livery |
| --- | --- | --- | --- | --- | --- |
| BL26 | Bob Hawke | 83-1010 | March 1983 | Standard | Pacific National blue & yellow |
| BL27 |  | 83-1011 | August 1983 | Standard | Pacific National blue & yellow |
| BL28 |  | 83-1012 | September 1983 | Standard | Pacific National blue & yellow |
| BL29 |  | 83-1013 | October 1983 | Broad | Pacific National blue & yellow |
| BL30 |  | 83-1014 | December 1983 | Standard | Pacific National blue & yellow |
| BL31 |  | 83-1015 | November 1983 | Standard | Pacific National blue & yellow |
| BL32 |  | 83-1016 | February 1984 | Broad | National Rail orange & grey |
| BL33 |  | 83-1017 | April 1984 | Standard | Pacific National blue & yellow |
| BL34 |  | 83-1018 | June 1984 | Broad | Pacific National blue & yellow |
| BL35 |  | 83-1019 | July 1984 | Standard | Pacific National blue & yellow |
Question:
how many locomotives entered service after the bl31?
Answer:
4