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:       Would you mind going to dinner with me tonight ?  
 Person2:I'd love to go out with you , but I'm sorry I'm busy tonight , but I'd like a rain check .  
 Person1:        OK . 

informal