I need some help in figuring out what I did wrong with this problem.

Question:
Given binary string representation of a positive integer find how many operations would it take to convert that number to 0. The operation can either be dividing the number by 2 if the number is even or subtracting 1 if the number is odd.

My code:-

def findNoOfOperations(s):
  num = int(s, 2)
  noOfOperations = 0
  while num:
    if num%2:
      num= num-1
    else:
      num//=2
    noOfOperations+=1
  
  return noOfOperations;

print(findNoOfOperations("10") == 2)
print(findNoOfOperations("1111") == 7)

I mentioned the time complexity as O(number of bits needed to represent the number) + O(logarithm of the integer value to the base 2) which finally boils down to O(logn), where n is the integer value(Correct me if I am wrong, as number of bits needed to represent is logn). The recruiter sent me an e-mail mentioning that I was rejected quoting, the solution I gave was suboptimal. It was an online assessment, and nowhere it was mentioned that I couldn't convert the binary string to integer value. How would you people approach this? What have I done wrong here?