def getmax(s):
    res = 0
    for i in xrange(46):
        cnt = 0
        for si in s:
            if si == "o": cnt += 1
            else:
                res = max(res, cnt)
                cnt = 0
        res = max(res, cnt)
    return res
    
D = int(raw_input())
s = ["x"] * 16 + list(raw_input() + raw_input()) + ["x"] * 16
ans = getmax(s)
for d in xrange(1, D + 1):
    for i in xrange(46):
        if "xo" in s[i:i + d] and "ox" in s[i:i + d]: continue
        ss = s[:]
        ss[i:i + d] = "o" * d
        ans = max(ans, getmax(ss))
print ans