Plotting multiple lines on a single graph using Shiny and ggplot2

I'm trying to build an app that will let the user plot multiple lines on a single graph. My data contains tourism data on multiple country by years.

> head(tourism)
  years Bulgaria Czech Republic   Denmark   Poland   Sweden   Norway
1  1995 5437.963       10274.98  9651.070 5523.500 7860.659 7294.971
2  1996 5921.961       13640.53 10810.187 5594.191 7716.620 7236.490
3  1997 5476.931       14932.49 10918.596 7579.637 7658.900 7243.111
4  1998 5197.050       16218.00 10287.564 7229.771 8029.087 7868.735
5  1999 4382.405       16125.00  9965.684 5644.924 8600.785 7814.983
6  2000 5170.091       15597.09 10005.887 6891.283 8654.086 7468.899

Now I'm trying to plot the data with the 'years' column as the x-axis and the other columns as the y-axis.

ui = fluidPage(
  titlePanel("Tourism"),
  sidebarLayout(
    sidebarPanel(
      selectizeInput("cnt",
                  "Select Country:",
                  choices = c("Bulgaria", 
                              "Czech Republic",
                              "Denmark",
                              "Poland",
                              "Sweden",
                              "Norway"),
                  selected = "Bulgaria",
                  multiple = TRUE
    )
    ),
    mainPanel(
      plotOutput("plot")
    )
  ) 
)


server = function(input, output) {

  output$plot = renderPlot({
    ggplot(tourism) +
      geom_line(mapping = aes(x = years, y = tourism[,input$cnt], colour = input$cnt)) + 
      labs (x = "Years", y = "Nights spent per 1000", title = "Tourism") + 
      scale_colour_discrete(name = "Country")
  })

}

shinyApp(ui = ui, server)

The problem is, if I try to plot more than one country at a time, I get the following error: "Aesthetics must be either length 1 or the same as the data (21): x, y, colour".

While searching, I figured that I'm missing an observe or reactive part, but I just cant figure out how to add it.

Any help would be appreciated.