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:       Now , you are to board the plane.We ' re sorry that we haven't done much to help you when you stayed in China .  
 Person2:I appreciate what you have done for me.Everything I have seen here has left a deep impression on me . I really don't know how to express my thanks to you .  
 Person1:        We are ready to help you .  
 Person2:Will you be kind to say " Thank you " to Mr.Zhang and other friends for me ?  
 Person1:        I'd like to . I'm sure your visit will help to promote the friendship and understanding between both of us.Welcome to China again .  
 Person2:Of course , I will.Well , it's time for me to say goodbye.The plane will take off soon.Hope some day you will come to America for a visit .  
 Person1:        Thank you . I will if I have chance.Goodbye and happy landing !  
 Person2:Goodbye ! 

informal