Python Text File Questions: When you type a number, you add the numbers in the file to save them to the file

# If there is only one number written in text.txt,
with open('text.txt', 'r') as txt:
    N1 = txt.read()   # N1 = '1'
N2 = int(N1) + 11    # N2 = 12
with open('text.txt', 'w') as txt:
    When you open txt.write(str(N2) #text.txt, the number 12 is entered