text: # Ivan Carvalho
  # Solution to https://www.urionlinejudge.com.br/judge/problems/view/1071
  #!/usr/bin/env python2.7
  # encoding : utf-8
  a = int(raw_input())
  b = int(raw_input())
  x,y = sorted([a,b])
  if x % 2 == 1:
  	x += 2
  else :
  	x += 1
  print sum(range(x,y,2))
  