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 .  
 Person2:Hi , Mary , Hi , Ken I hate to bring this up , but that new stereo , system you got ...  
 Person1:        Yeah ?  
 Person2:You were playing it very late last night .  
 Person1:        Yeah ?  
 Person2:It kept me awake .  
 Person1:        Oh , I'm sorry .  
 Person2:It kept me awake a couple of hours .  
 Person1:        I'm so sorry , I .. I didn't realize it was that loud .  
 Person2:It was that loud , and it was pretty late , and check with Mary if you don't believe me .  
 Person1:        It's true.It was a bit loud .  
 Person2:I'm very sorry . I didn't realize it . I promise I'll keep it down in the future .  
 Person1:        Oh , it's no problem.It ' s OK.You know , it only happened once .  
 Person2:I am glad we've straightened everything out . 

informal