D = int(input())
C = ['x']
C.extend([c for c in input()])
C.extend([c for c in input()])
C.extend(['x'] * (D + 1))

max_holiday = D
for i in range(1, 16):
    cnt = 0
    j = 1
    while C[i - j] == 'o':
        cnt += 1
        j -= 1
    cnt += d
    j = d
    while C[i + j] == 'o':
        cnt += 1
        j += 1
    max_holiday = max(max_holiday, cnt)

print(max_holiday)