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:       Good evening , Mr . Wu .  
 Person2:Good evening , Mr . Smith .  
 Person1:        Have you met my wife , Mary ?  
 Person2:No . I haven ’ t had the pleasure .  
 Person1:        Mary , this is Mr . Wu , my new Chinese friend .  
 Person2:How do you do , Mr . Wu ? Welcome .  
 Person1:        How do you do ?  
 Person2:Have a glass of wine , Mr . Wu ? And let me introduce you to some of my guests . 

informal