import math
import sys
from typing import List, Tuple

int1 = lambda x: int(x) - 1
input = lambda: sys.stdin.readline().rstrip('\n')
ii = lambda: int(input())
vi = lambda: list(map(int, input().split()))
vi1 = lambda: list(map(int1, input().split()))


def dbg(*args, **kwargs):
    print(*(repr(arg) for arg in args), *(f'{k}: {repr(v)}' for k, v in kwargs.items()),
          sep='; ', file=sys.stderr, flush=True)


def main():
    d = ii()
    a = 'x' * d + input() + input() + 'x' * d

    ans = 0
    for i in range(len(a)):
        for j in range(i + 1, len(a) + 1):
            s = a[i:j]
            if sum(v == 'x' for v in s) <= d and 'o' not in s.lstrip('o').rstrip('o'):
                ans = max(ans, j - i)
    return ans


def _start():
    if (ret := main()) is not None:
        print(*ret) if isinstance(ret, List) or isinstance(ret, Tuple) else print(ret)


if __name__ == '__main__':
    _start()