n = int(input())
t = "x"*15+input()+input()+"x"*15
ans = 0
for i in range(50):
    for c in range(1,n+1):
        if t[i:i+c] != "x"*c: continue
        s = t[:i] + "o"*c + t[i+c:]
        v = 0
        for i in s:
            if i == "o":
                v += 1
            else:
                ans = max(ans,v)
                v = 0
print(ans)