In United States, when two strange people meet in the street, they say "How do you do!" each other. Now, you go to the steet.If you meet a man/woman, you should say "How do you do!" to him/her.

You will meet many people.One people's name one line.The input "back" means the end of input.

you should say "How do you do!" to each people.No say to "back".

yhr