Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given n orders, each order consists of a pickup and a delivery service.
Count all valid pickup/delivery possible sequences such that delivery(i) is always after of pickup(i). 
Since the answer may be too large, return it modulo 10^9 + 7.
 
Please complete the following python code precisely:
```python
class Solution:
    def countOrders(self, n: int) -> int:
```