def main():
    N, M = map(int, input().split())
    keys = [list(input()) for _ in range(N)]
    keys_t = [list(elm) for elm in zip(*keys)]
    not_have_keys = list(map(lambda elm: elm.count("x"), keys_t))
    print(max(not_have_keys)+1)


if __name__ == "__main__":
    main()