import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 19
MOD = 10 ** 9 + 7
EPS = 10 ** -10

def RLE(data):
    """ ランレングス圧縮 """
    from itertools import groupby

    return [(x, len(list(grp))) for x, grp in groupby(data)]

D = INT()
N = 42
S = 'x'*14
S += input()
S += input()
S += 'x'*14

rle = [('o', 0)] + RLE(S) + [('o', 0)]
M = len(rle)
ans = 0
for i in range(1, M-1, 2):
    s0, ln0 = rle[i-1]
    s1, ln1 = rle[i]
    s2, ln2 = rle[i+1]
    if ln1 <= D:
        ans = max(ans, ln0+ln1+ln2)
    else:
        ans = max(ans, ln0+D, D+ln2)
print(ans)