mod = 998244353


def main():
    import sys
    input = sys.stdin.readline

    N = int(input())
    S = "." + input().rstrip('\n')

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

    print(ans)


if __name__ == '__main__':
    main()