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:
| Rank | Swimmer | Country | Time | Note |
| --- | --- | --- | --- | --- |
| 1 | Claudia Poll | Costa Rica | 57.43 | Q |
| 2 | Vanessa García | Puerto Rico | 57.95 | Q |
| 3 | Arlene Semeco | Venezuela | 58.11 | Q |
| 4 | Heysi Villarreal | Cuba | 58.67 | Q |
| 5 | Maríana Álvarado | Mexico | 58.69 | Q |
| 6 | Carolina Moreno | Mexico | 59.11 | Q |
| 7 | Isabella Tafur | Colombia | 59.70 | Q |
| 8 | Ximena Maria Vilár | Venezuela | 59.79 | Q |
| 9 | Nikia Hillarie | Bahamas | 59.92 |  |
| 10 | Sharon Fajardo | Honduras | 1:00.45 |  |
| 11 | Maria Álvarez | Colombia | 1:00.76 |  |
| 12 | Alia Atkinson | Jamaica | 1:01.17 |  |
| 13 | Alexis Jordan | Barbados | 1:01.79 |  |
| 14 | Sharntelle McLean | Trinidad and Tobago | 1:03.26 |  |
| 15 | Jennifer Powell | Cayman Islands | 1:03.41 |  |
| 16 | Nishani Cicilson | Suriname | 1:03.88 |  |
| 17 | Sade Daal | Suriname | 1:04.70 |  |
| 18 | Dalia Tórrez | Nicaragua | 1:05.69 |  |
| -- | Gisela Morales | Guatemala | DNS |  |
| -- | Alana Dillette | Bahamas | DNS |  |
| -- | Pamela Benítez | El Salvador | DNS |  |
| -- | Nilshaira Isenia | Netherlands Antilles | DNS |  |
Question:
how many swimmers did not swim?
Answer:
4