Calculate the median of the following data set.
The median is the middle value of a data set when it is sorted in ascending order. If there are an even number of values, then the median is the average of the two middle values. In the given input, there are six numbers, so the median is the average of the two middle values, 4 and 5. Hence, the median of the given data set is (4 + 5) / 2 = 4.5.
1, 2, 4, 5, 8, 9
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:
Calculate the median of the following data set.

### Input:
1, 2, 4, 5, 8, 9

### Response:
The median is the middle value of a data set when it is sorted in ascending order. If there are an even number of values, then the median is the average of the two middle values. In the given input, there are six numbers, so the median is the average of the two middle values, 4 and 5. Hence, the median of the given data set is (4 + 5) / 2 = 4.5.