func main()
	var _: [][]char :: cui@input().split(" ")
	var A: int :: _[0].toInt(&)
	var B: int :: _[1].toInt(&)
	var C: int :: _[2].toInt(&)
	var D: int :: _[3].toInt(&)
	var ans: int
	for x(A, B)
		for y(C, D)
			do ans :+ x = y ?(0, 1)
		end for
	end for
	do cui@print("\{ans}\n")
end func