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:       Hi , Celia ! How was your trip to the United States ?  
 Person2:It was terrific . I really enjoyed it .  
 Person1:        Great . How long were you away ?  
 Person2:I was there for about three weeks .  
 Person1:        That's a long time ! Was the weather OK ?  
 Person2:Yes , most of the time . But it snowed a lot in Chicago .  
 Person1:        So , what was the best thing about your trip ?  
 Person2:Oh , that's difficult to say . But I guess I liked Nashville the best . 

informal