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:       Here's 30 yuan for my ticket .  
 Person2:Keep it . I'm buying tonight .  
 Person1:        No , you can't do that .  
 Person2:Sure I can , my treat . 

informal