# leetle

## 37. Count Prime Numbers

Write a function `solve` that counts the number of prime numbers less than n.

**Example:**  
`Input: 10`  
`Output: 4`  
`Explanation: 2, 3, 5, 7 are prime numbers less than 10`

Make sure you `return` your solution, don't print!

```python

def solve(n):
    pass
```