An integer N (1 ≤ N ≤ 70), representing some quantity or size.
An integer K (1 ≤ K ≤ 70), representing some quantity or size.
A string s of length K, consisting of characters 'r' and 'b'.

### Example Input:
```
12 2
rb
```

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