def _find_str(s: str, char: str) -> int:
    """
    Finds a sequence within a string, and returns the position. If not exists, returns ``-1``.

    :param s: Latex string code
    :param char: Sequence
    :return: Position
    """
    index = 0

    if char in s:
        c = char[0]
        for ch in s:
            if ch == c:
                if s[index:index + len(char)] == char:
                    return index

            index += 1

    return -1