Given the task definition and input, reply with output. 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'.

 Person1:       Well , Mike , nowadays there's much talk about nanometer . But what on earth is it ?  
 Person2:Nanometer is a length scale . It's one billionth of a meter , roughly ten times the size of an individual atom .  
 Person1:        Hmm ... it's hard to figure out the exact size , I'm afraid .  
 Person2:Well , let's make it this way . For comparison , 10 NM is 1000 times smaller than the diameter of a human hair . There are as many nanometers in an inch as there are inches in 400 miles .  
 Person1:        I see.Thank you . 

informal