def METHOD_NAME():
    """
    Very Important:
    Exactly two characters are available for each quantum number. Therefore, half
    integer quanta are rounded up ! In addition, capital letters are used to
    indicate quantum numbers larger than 99. E. g. A0 is 100, Z9 is 359. Small
    types are used to signal corresponding negative quantum numbers.
    """
    # examples from the docs
    assert parse_letternumber("A0") == 100
    assert parse_letternumber("Z9") == 359
    # inferred?
    assert parse_letternumber("z9") == -359
    assert parse_letternumber("ZZ") == 3535