func main()
	var z: [][]char :: cui@input().split(" ")
	var a: []int :: [z[0].toInt(&),z[1].toInt(&),z[2].toInt(&),z[3].toInt(&)]
	do a.sort()
	if(a[1]-a[0] = 1 & a[2]-a[1] = 1 & a[3]-a[2] = 1)
		do cui@print("Yes\n")
	else
		do cui@print("No\n")
	end if
end func