ui <- fluidPage(
        sliderInput("n", "Number of observations", 2, 1000, 500),
        plotOutput("plot")
    )
    
    server <- function(input, output) {
        autoInvalidate <- reactiveTimer(1000)
        output$plot <- renderPlot({
            autoInvalidate()
            hist(rnorm(isolate(input$n)))
        })
    }
    
    shinyApp(ui, server)