Definition: You are given a conversation between two people. 'Person1:' and 'Person2:' are used to separate their respective dialogues. You are required to assign a label 'formal' if there is an absence of emotion and a presence of questions anywhere within the conversation. If such pattern is not found assign the label 'informal'.
Input:  Person1:       Thank you.Steven.That was the most magnificent meal I've had abroad.You ' ll have to let me reciprocate the next time you're in Beijing . 
 Person2:Don't worry about it , Lin.That ' s no big deal.You know , Americans appreciate China's rich culinary culture . Just excuse me for a second while I check the number here and figure out how much to give the waiter.Hmm , by the way , what do you do about tipping in China ? 
 Person1:        We don't . 
 Person2:No tipping ? Now that's what I call a civilized system . 
 Person1:        At hotels and some restaurants they add a service charge to the bill , but other than that , tipping isn't customary . 
 Person2:What about cab drivers and porters ? 
 Person1:        In a cab you just pay what it says on the meter . I generally tip hotel porters 10 yuan per bag , but in first-class hotels they're instructed not to accept gratuities . 
 Person2:You'd have a revolution on your hands if you tried to introduce that sort of system here . 

informal