An integer N (1 ≤ N ≤ 3000), representing the length of a string s.
A string s of length N, consisting of lowercase English letters.
An integer M (1 ≤ M ≤ 3000), representing the length of a string t.
A string t of length M, consisting of lowercase English letters.

### Example Input:

```
5
axyb
5
abyxb
```

### Function Signature:
Write a function f(N, s, M, t) that takes in the input.
def f(N: int, s: str, M: int, t: str):
    '''
    N: an integer
    s: a string
    M: an integer
    t: a string
    '''