def calcs(x,y,ax,ay,bx,by) ((ax-x)*(by-y)-(bx-x)*(ay-y))/2.0 end def inpf() a=gets.chomp.split(" ").map(&:to_f)end def inps() a=gets.chomp.split(" ")end def copy(a) Marshal.load(Marshal.dump(a)) end def factorial(n)(n < 2)? 1 : (2..n).inject(:*) end def scount(a) b=na(a.max+1);a.each{|n|b[n]+=1};return b end def na(n,d=0) Array.new(n,d)end def na2(n,m,d=0) Array.new(n){Array.new(m,d)}end def na3(n,m,l,d=0) Array.new(n){Array.new(m){Array.new(l,d)}}end def bit(n) n.to_s(2).split("").map(&:to_i) end def inp() a=gets.chomp.split(" ").map(&:to_i)end a,b=inp ans = 0 (a..b).each do |c| ans += 1 if(((a+b+c)/3.0 - (a+b+c)/3) <= 10**-20) end p ans