The table below shows the number of unique visitors to a website over five months.
| Month | Visitors |
|---|---|
| March | 12,500 |
| April | 11,800 |
| May | 13,200 |
| June | |
| July | 12,000 |
If the mean number of unique visitors per month for these five months was 12,300, what was the number of visitors in June?