func main()
	var ss: [][]char :: cui@input().split(" ")
	var a: int :: ss[0].toInt(&)
	var b: int :: ss[1].toInt(&)
	var c: int :: ss[2].toInt(&)
	var d: int :: ss[3].toInt(&)
	var ans: int :: 0
	for x(a, b)
		for y(c, d)
			do ans :+ x <> y ?(1, 0)
		end for
	end for
	do cui@print("\{ans}\n")
end func