An integer N (1 ≤ N ≤ 52), representing some quantity or size.
A string S1 of length N, consisting of lowercase and uppercase English letters.
A string S2 of length N, consisting of lowercase and uppercase English letters.

### Example Input:

```
3
aab
ccb
```

### Function Signature:
Write a function f(N, S1, S2) that takes in the input.
def f(N: int, S1: str, S2: str):
    '''
    N: an integer
    S1: a string
    S2: a string
    '''