The challenge provides us with a python script bells.py. Running this script it asks for a number and tells us the outcome. Looking at the script it will display "Nice you got it, your flag is the value you initally got in the form 'uiuctf{NUMBER_YOU_GOT}'" If the correct number is entered. There's basically just a bunch of calculations and conversions going on with a set final string which is expected 'Lmao'. It is now possible to work back from that to get to the number of bells Tom Nook has;

Tools used:

• windows calculator (with scientific notations enabled)
• http://www.asciitable.com/

Read the code and comments from bottom to top, as I started with the expected outcome 'Lmao' and worked my way back to what guess is expected. Inbetween every processing step I have included the content(s) of guess.

print('Input a Number Below to guess how many bells Tom Nook has :)')
guess = None
try:
  guess = int(input())
except:
  print("No silly that is wrong, you need a number.")
  exit()
try:
    # guess = 1293869277 -> flag: uiuctf{1293869277}
    # -2410619
    for tax3 in range(0,1234):
        guess -= 1337 + tax3

    # guess = 1291458658
    guess = str(hex(int(guess)))[2:] # convert the integer to a hexadecimal string
    
    # guess = '4CFA1862'
    # split the string in two and put the last 4 character before the first 4 characters
    guess = str(guess[4:8]) + str(guess[0:4])
    
    # guess = '18624CFA'
    guess = int(guess,16) # interpret guess as hexadecimal thus converting to an integer
    
    # guess = 409095418
    for tax4 in range(18,30,2): 
        guess = int((str(hex(guess)[2:])[::-1]),16) - tax4 * 1000 # magic
        # final step (28) to get to 457253818 to determine logic:
        # -(28 * 1000) guess = 457281818               :add tax
        # convert that to hex: 1B41911A                :to hex
        # reverse that hexadecimal string: A11914B1    :reverse
        # which is 2702775473                          :to dec
        #
        # reversing the remaining steps:
        #                  add tax               to hex      reverse     to dec  
        # 26: 2702775473 + 26000 = 2702775473 -> A1197A41 -> 14A7911A -> 346525978
        # 24: 346525978  + 24000 = 346549978  -> 14A7EEDA -> ADEE7A41 -> 2918087233
        # 22: 2918087233 + 22000 = 2918109233 -> ADEED031 -> 130DEEDA -> 319680218
        # 20: 319680218  + 20000 = 319700218  -> 130E3CFA -> AFC3E031 -> 2948849713
        # 18: 2948849713 + 18000 = 2948849713 -> AFC42681 -> 18624CFA -> 409095418
   
    # guess = 457253818
    # -5970000
    for tax5 in range(0,1000,5):
        for tax4 in range(10,40,10):
            guess -= tax5 * tax4 
    
    # guess = 451283818
    guess = str(hex(guess)[2:]) # convert to hexadecimal
    
    # guess = '1AE60B6A'
        # split the string per 2 characters and convert them from hex into a decimal array
    guess = [int(guess[i:i+2],16) for i in range(0,len(guess),2)] 
    
    # guess = [26, 230, 11, 106]
    # sorting the caculations per array element and having them line by line:
    guess[0] *= 3 # *3
    guess[0] += int((ord('j') - ord('J')) / (ord('E') - ord('e'))) # -1
    guess[0] += int((ord('g') - ord('G')) / (ord('z') - ord('Z')) * ord('c') - ord('a')) # +2
    
    guess[1] /= 2  # /2
    guess[1] -= 18 # -18
    
    guess[2] += ord('b') # +98
    
    guess[3] -= 30 # -30
        
    # guess = [79, 97, 109, 76]
    guess = [hex(int(g)) for g in guess][::-1] # reverse the array and convert from int to hex
    
    # guess = ['4C','6D','61','4F']
    guess[3] = hex(int(guess[3],16) + 32) # +32 for guess[3]

    # guess = ['4C','6D','61','6F'] ('L','m','a','o')
    final = ''
    for i in range(len(guess)):
        final += chr(int(guess[i],16)) # convert the array entries from hex to character and form them into a string

    if final == 'Lmao':
        print("Nice you got it, your flag is the value you initally got in the form 'uiuctf{NUMBER_YOU_GOT}'")
    else:
        print("Good try but your ending value was " + final + " try again <3")
        print("\n")
except:
    print("Your guess was so wrong you broke the guessing machine. Good try, but try again <3")