d = int(input())
c = input() + input()
ans = 0
for i in range(14):
    longest = 0
    current = 0
    fst = True
    for j in range(14):
        if (i <= j < i + d and fst) or c[j] == 'o':
            current += 1
        else:
            current = 0
        longest = max(longest, current)
        if i <= j and c[j] == 'o':
            fst = False
    ans = max(ans, longest)
print(ans)