d = int(input())
C = input() + input()

bef = "o"
lst = []
cnt = 0
for c in C:
    if c != bef:
        lst.append(cnt)
        cnt = 1
        bef = c
    else:
        cnt += 1

lst.append(cnt)
if bef == "x":
    lst.append(0)

l = len(lst)
ans = 0
for i in range(1, l, 2):
    if lst[i] <= d:
        ans = max(ans, lst[i - 1] + lst[i] + lst[i + 1])
    else:
        ans = max(ans, max(lst[i - 1], lst[i + 1]) + d)
print(ans)