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:
| Date | Number | Type | Captain | Casualties | Sunk by |
| --- | --- | --- | --- | --- | --- |
| 4 May 1943 | U-209 | VIIC | Heinrich Brodda | 46 | Catalina Flying-boat of No. 5 Squadron RCAF |
| 5 May 1943 | U-638 | VIIC | Oskar Staudinger | 44 | HMS Sunflower |
| 5 May 1943 | U-531 | IXC/40 | Herbert Neckel | 54 | HMS Vidette |
| 6 May 1943 | U-192 | IXC/40 | Werner Happe | 55 | HMS Loosestrife |
| 6 May 1943 | U-125 | IXC | Ulrich Folkers | 54 | HMS Oribi, HMS Snowflake |
| 6 May 1943 | U-630 | VIIC | Werner Winkler | 47 | HMS Vidette |
| 6 May 1943 | U-438 | VIIC | Heinrich Hensohn | 48 | HMS Pelican |
Question:
how many captains are listed?
Answer:
7