def trans(c):
    if c == "#":
        return 1
    else:
        return 0

N = int(input())
S = list(input())
S = list(map(trans, S))

cnt = 0
ans = 0
for i in range(N - 1, -1, -1):
    if S[i]:
        ans = max(ans, N - i + cnt)
        cnt += 1
    else:
        cnt = max(0, cnt - 1)
print(ans)