What is the sentinel value in the following code?import random def chatter$)$:greetings $=["$Hello$!",$ "What's up$?!",$ "Howdy!", "Greetings!"$]$goodbyes $=["$Bye$!",$ "Goodbye!", "See you later!", "See you soon!"$]$keywords $=["$black$",$ "green", "oolong", "white"$]$responses $=["$$$5","$$$6","$$$7","$$$8"]$print$($random$.$choice$($greetings$))$user $=$ input$("$What tea do you want? $($or type bye to quit$)$: $")$user $=$ user.lower$)$while $($user $!=$ "later"$)$:keyword$\_$found $=$ Falsefor index in range$($len$($keywords$))$: if $($keywords$[$index$]$ in user$)$:print$("$Price is: $"+$ responses$|$index$])$keyword$\_$found $=$ Trueif $($keyword$\_$found $==$ False$)$:new$\_$keyword $=$ input$("$I$\text{'}$m not sure how to respond. What keyword should I respond to$?")$keywords$.$append$($new$\_$keyword$)$new$\_$response $=$ input$("$How should I respond to$"+$ new$\_$ keyword $+"?")$responses$.$append$($new$\_$response$)$user $=$ input$("$What tea do you want? $($or type later to quit$)$:$")$user $=$ user.lower$)$print$($random$.$choice$($goodbyes$))$byeGoodbye$!$later $!$