import itertools

D = int(input())
C = itertools.groupby('x' * 14 + input() + input() + 'x' * 14)
L = [0]
for c in C:
    L.append(len(list(c[1])))
L.append(0)

ans = D
for i in range(1, len(L) - 1, 2):
    if D >= L[i]:
        ans = max(ans, L[i - 1] + L[i] + L[i + 1])
    else:
        ans = max(ans, L[i - 1] + D, D + L[i + 1])
print(ans)