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:
| Poll Source | Date(s) administered | Sample size | Margin of Error | Mel Martinez (R) | Betty Castor (D) |
| --- | --- | --- | --- | --- | --- |
| Zogby International | October 31 | 600.0 | ± 4.0% | 46% | 46% |
| Quinnipiac University | October 31 | 1098.0 | ± 3.0% | 49% | 44% |
| CNN / USA Today / Gallup | October 28 | 1138.0 | ± 4.0% | 46% | 48% |
| Mason Dixon | October 26 | 625.0 | ± 4.0% | 47% | 46% |
| New York Times | October 23 | 802.0 | ± 3.0% | 44% | 47% |
| Quinnipiac University | October 22 | 944.0 | ± 3.2% | 49% | 46% |
| Insider Advantage | October 22 | 400.0 | ± 5.0% | 46% | 44% |
| Survey USA | October 22 | 741.0 | ± 3.7% | 47% | 50% |
| Miami Herald | October 19 | 800.0 | ± 3.5% | 44% | 44% |
| Research 2000 | October 18 | 600.0 | ± 4.0% | 48% | 48% |
| Quinnipiac University | October 15 | 808.0 | ± 3.5% | 47% | 47% |
| Survey USA | October 15 | 596.0 | ± 4.1% | 49% | 47% |
| Mason-Dixon | October 14 | 625.0 | ± 4.0% | 45% | 45% |
| UNF | October 10 | 641.0 | ± 4.0% | 35% | 38% |
| Mason-Dixon | October 4 | 625.0 | ± 4.0% | 46% | 41% |
| Quinnipiac University | October 1 | 706.0 | ± 3.8% | 48% | 47% |
| Survey USA | October 1 | 706.0 | ± 3.8% | 50% | 46% |
| Gallup | Sept. 18 | 674.0 | ± 4.0% | 45% | 51% |
| Quinnipiac University | Sept. 18 | 819.0 | ± 3.4% | 42% | 43% |
| Survey USA | Sept. 12 | 602.0 | ± 4.1% | 45% | 49% |
| Rasmussen Reports | August 24 | 500.0 | ± 4.5% | 44% | 44% |
Question:
What is the highest sample size administered on October 18?
Answer:
600.0