number = int(input("Enter a positive 3-digit number: "))
firstDigit = number // 100
secondDigit = (number - (firstDigit * 100))//10
lastDigit = number - ((firstDigit * 100) + (secondDigit * 10))
newNum = (lastDigit*100) + (secondDigit*10) + firstDigit
print(newNum)
I think this is what you want