D = int(input())
C = list(input()) + list(input()) + ["x"] * D
ans = 0
for i in range(1, 15):
    if "o" * i in "".join(C):
        ans = max(ans, i)
for st in range(15):
    l = 0
    for i in range(1, D + 1):
        if "x" * i == "".join(C[st: st + i]):
            l = max(l, i)
    E = []
    for i in range(len(C)):
        if st <= i < st + l:
            E.append("o")
        else:
            E.append(C[i])
    for i in range(21, 0, -1):
        if "o" * i in "".join(E):
            ans = max(ans, i)
            break
print(ans)