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.Brown . 
 Person2:Good evening , David.Good evening , Mary.It ' s so good of you both to come . 
 Person1:        It's nice of you to invite us . 

informal