Totally speaking, this contest is very funny.I worked out the first four problems finally.Now is the summary:

Problem A: Input a number and output a string.So what string will be right? After looking the sample test,we can see the whole results which are the name of American Presidents and correspond to the order in American history. So we can draw a conclusion：just list the first forty American Presidents.And what you should pay attention to is just to output the last name.As a result,the results will be one word except for "Van Buren".

Problem B: Input two numbers and output a number with a QR code. This is a simple problem.You will see a two-dimensional matrix filled with 0 or 1 after scanning the QR code.It's not hard to see the two numbers (a1 and a2) meaning the row number and column number of the matrix.You just output the corresponding result.

Problem C: The description is several words.I still don't understand what it means after skimming twice. Finally,I see the description is a program which is written by LOLCODE. With the help of a magic website which is introducing LOLCODE,I understand this program finally. The address of the magic website

Problem D: This problem is similar to Problem C but the description is a picture in replace of text. It's not very hard to read this program.Here is a point:the icon of a snake or a arrow or a smile or a heart is standing for just a variable.