An integer N (1 ≤ N ≤ 1000), representing some quantity or size.
An integer L (1 ≤ L ≤ 30), representing some length.
A list of N strings, each of length L, consisting of lowercase English letters.

### Example Input:

```
4 2
oi
io
rr
rr
```

### Function Signature:
Write a function f(N, L, strings) that takes in the input.
```python
def f(N: int, L: int, strings: List[str]):
    '''
    N: an integer
    L: an integer
    strings: a list of strings
    '''
```