D = int(input())
C = input() + input()

result = 0
for i in range(14 - D):
    t = list(C)
    j = i
    while t[j] == 'x' and j < 14:
        t[j] = 'o'
        j += 1
    result = max(result, max(len(a) for a in ''.join(t).split('x')))
print(result)