def validateDurString(s):
    """
    Utility method to enforce an IB requirement.
    """
    d = ['S', 'D', 'W', 'M', 'Y']
    sp = s.split()
    if len(sp) != 2:
        return False
    if sp[1] not in d:
        return False
    try:
        int(sp[0])
    except ValueError:
        return False
    return True
