How can I add point with geom_point according to equilibrium point?

Question

I tried to apply economic order quantitz which I need to visualize. However, I would like to indicate equilibrium points in economic order quantity where I have overlapped lines. Unfortunately,

eq <- xx[which.min(abs(xx$holdingcost - xx$orderingcost)), ]

this part is not working exaclty. It does not put point at equilibrium point everytime.

Here is the code.

ui.R

  library(shiny)

  shinyUI(pageWithSidebar(

  headerPanel("Economic Order Quantity"),

   sidebarPanel(
 h3(strong("Parameters",style = "color:black")),
 br(),

  sliderInput("D", "Annual Demand Quantity (D)",min = 1, max = 1000, step= 10, value = 500),
  sliderInput("S", "Ordering Cost (S)",min = 1, max = 1000, step= 1, value = 500),
  sliderInput("h", "Holding Cost (i)",min = 0.01, max = 1, step= 0.01, value = 0.3),
  sliderInput("C", "Cost per unit (c) ",min = 1, max = 500, step= 1, value = 150)

  ),

   mainPanel(

         plotOutput("plotgraph1"))))

server.R

 library(shiny)
 require(ggplot2)
 require(scales)

shinyServer(function(input, output) {

output$plotgraph1<-renderPlot({

    Q<-((2*input$D*input$S)/(input$h*input$C))^(1/2)
    xdata <- seq(1,Q*(1.7),1)

    HCOCdata <- matrix(1,1)
    HCdata <- matrix(1,1)
    OCdata <- matrix(1,1)

  for (i in xdata) {

      OC<-(input$D/i)*input$S
      HC<-(i/2)*input$h*input$C
      HCOC<-OC+HC
      HCdata[i]<- HC
      OCdata[i]<- OC
      HCOCdata[i]<- HCOC
}


    HCOCcost <- data.frame(HCOCcost=HCOCdata)
    holdingcost <- data.frame(holdingcost=HCdata)
    orderingcost <- data.frame(orderingcost=OCdata)

    Quantity <- xdata
    CostType <- c("HCOCcost","holdingcost","orderingcost")
    xx<-cbind(Quantity,HCOCcost,holdingcost,orderingcost)


    y <- ggplot(xx, aes(x=Quantity, y=Cost), group = xx , colour=xx ) + 
        geom_line(size=1,aes(y=HCOCcost, colour = "HCOCcost"), linetype=2) + geom_line(size=1,aes(y=holdingcost, colour = "holdingcost")) + geom_line(size=1,aes(y=orderingcost, colour = "orderingcost")) 

    eq <- xx[which.min(abs(xx$holdingcost - xx$orderingcost)), ]
    y1 <- y + scale_y_continuous(limits=c(0, max(HCOCcost)/10),labels=comma) + geom_point(data = eq, aes(y = holdingcost), size = 4 , color="red") 
    y1 })})