n = int(input())
t = "x"*14+input()+input()+"x"*14
ans = 0
for i in range(50):
    if t[i:i+n] != "x"*n: continue
    s = t[:i] + "o"*n + t[i+n:]
    v = 0
    for i in s:
        if i == "o":
            v += 1
        else:
            ans = max(ans,v)
            v = 0
print(ans)