def make_position_string(length):
    """
    Takes the length of the state and returns a string 01234... to be
    displayed in the interaction to make it easier for the user to pick
    the position of the pair to be moved.
    
    make_position_string(int) -> string
    """
    string = ""
    for i in range(0,length):
       if i < 10:
           string = string + str(i)
       else:
           string = string + str(i)[-1]
    return string