Detailed Instructions: 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'.
Q:  Person1:       I've really enjoyed your party , Lisa . 
 Person2:Not at all , Sam . 
 Person1:        I wish I could stay longer , but I must be going . 
A:
informal