server <- function(input, output) {
  output$distPlot <- renderPlot({
    hist(rnorm(input$obs), col = "darkgray", border = "white")
  })
}
ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      sliderInput(
        "obs",
        "Number of observations:",
        min = 10,
        max = 500,
        value = 100
      )
    ),
    mainPanel(plotOutput("distPlot"))
  )
)
shinyApp(ui = ui, server = server)