def _rotate_r(__s: str) -> str:
    return __s[-1] + __s[0:-1]


def _valid_rotate(__s: str, __c: str) -> bool:
    for sc, cc in zip(__s, __c):
        # can never rotate a "1" onto an "x"
        if sc == "x" and cc == "1":
            return False

    return True


def _fix_exes(__s: str, __c: str) -> str:
    result = ""

    for sc, cc in zip(__s, __c):
        if sc == "x":
            result += "x"

        elif cc == "x":
            result += "0"

        else:
            result += cc

    return result


def rotate_r(__s: str) -> str:
    result = _rotate_r(__s)

    while not _valid_rotate(__s, result):
        result = _rotate_r(result)

    return _fix_exes(__s, result)