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:       Thanks for lunch . It was delicious .  
 Person2:It's OK .  
 Person1:        Next time lunch is on me .  
 Person2:Don't be silly .  
 Person1:        I'm serious .  
 Person2:All right . Next time you will treat .  
 Person1:        It's a deal . 

informal