#!/usr/bin/python

class LengthAccumulator(object):
	def __init__(self):
		self.number = 1

	def __neg__(self):
		self.number += 1


class LengthLiteral(object):

	def __neg__(self):
		return LengthAccumulator()

	def __sub__(self, other):
		if isinstance(other, LengthAccumulator):
			return other.number + 1
		else:
			return 1


I = LengthLiteral()


if __name__ == "__main__":

	assert      I-I == 1
	assert     I--I == 2
	assert I------I == 6