Arithmetic with shiny input - r

Question

I have simulated annealing function which finds the global minimum. I am taking inputs from a shiny dashboard and I have radiobuttons to choose between minimise and maximise. I want to be able to find the global maximum by simply multiplying my input equation by -1. How can I do this arithmetic in shiny. Here is what I have so far but not sure what to put in the else if statement.
This is from the UI:
textInput("ObjectiveFun",
h3("Objective Function"),
value = "(x+2*y-7)^2+(2*x+y-5)^2"),
radioButtons("maxormin",
h3("Goal"),
choices=c("Minimise"="min", "Maximise"="max")),
This is from the server:
observeEvent(input$maxormin,{
if(input$maxormin == min)
{
Func <- input$ObjectiveFn
}
else if(input$maxormin == max)
{
#trying to get: Func <- input$-1*(ObjectiveFn)
}
})
Here is the entire shiny app so far:
library(shiny)
source("simulated_annealing.R")
ui <- fluidPage(
titlePanel("Simulated Annealing App"),
sidebarLayout(
position = "left",
sidebarPanel("User input",
textInput("ObjectiveFun",
h3("Objective Function"),
value = "(x+2*y-7)^2+(2*x+y-5)^2"),
radioButtons("maxormin",
h3("Goal"),
choices=c("Minimise"="min", "Maximise"="max")),
numericInput("XL",
h3("Lower bound of x"),
value = -5),
numericInput("XU",
h3("Upper bound of x"),
value = 5),
numericInput("YL",
h3("Lower bound of y"),
value = -5),
numericInput("YU",
h3("Upper bound of y"),
value = 5),
numericInput("TEMP",
h3("Starting temperature"),
value = 100),
numericInput("NEPOCHS",
h3("Number of epochs"),
value = 25),
numericInput("NITER",
h3("Maximum number of iterations per epoch"),
value = 8),
numericInput("AMIN",
h3("Minimum number of moves per epoch"),
value = 3),
sliderInput(
"ALPHA",
h3("Cooling rate"),
min=0,
max=1,
value=0.95,
step = NULL,
round = FALSE,
ticks = TRUE,
animate = FALSE,
width = NULL,
sep = ",",
pre = NULL,
post = NULL,
timeFormat = NULL,
timezone = NULL,
dragRange = TRUE
),
actionButton("Go","Simulate"),
),
mainPanel("System Outputs",
textOutput("value")
)
),
)
server <- function(input, output)
{
Sim <- eventReactive(input$Go, {
xlower <- input$XL
xupper <- input$XU
ylower <- input$YL
yupper <- input$YU
temp <- input$TEMP
alpha <- input$ALPHA
nepochs <- input$NEPOCHS
I <- input$NITER
A <- input$AMIN
observeEvent(input$maxormin,{
if(input$maxormin == min)
{
Func <- input$ObjectiveFn
}
else if(input$maxormin == max)
{
}
})
value <- simannealing(Func,goal,temp,I,A,alpha,nepochs,xlower,xupper,ylower,yupper)
paste("Final value is:", value[3],"at x value: ", value[1], "and y value: ", value[2])
})
output$FinalValues <- renderText({
Sim()
})