|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 competitors did not start the preliminaries?
Answer: 4