Create a multi.sj shiny widget with country flags in shiny app

Question

Im trying to create a multi.js shiny widget like this here. But I miss the flags object. Anyone knows where can I find and load it?

library(shiny)
library(shinyWidgets)
 countries<-c("Belgium","Greece","Brazil")

ui <- fluidPage(
  multiInput(
    inputId = "Id010",
    label = "Countries :", 
    choices = NULL,
    choiceNames = lapply(seq_along(countries), 
                         function(i) tagList(tags$img(src = flags[i],
                                                      width = 20, 
                                                      height = 15), countries[i])),
    choiceValues = countries
  )
)

server <- function(input, output) {
  
  
  
}

shinyApp(ui, server)