Do the following operations on a natural number: if its digital sum is odd, subtract 1 from it; if its digital sum is even, divide it by 2 and round, and so on until the number is 1. The number of operations performed is called the "quack number" of this natural number, so what is the smallest "quack number" among the natural numbers greater than 30.
对一个自然数作如下操作：如果它的数字和是奇数就把它减1；如果它的数字和为偶数就把它除以2再取整，如此进行直到得数为1．其中进行操作的次数称为这个自然数的"呱呱数"，那么在大于30的自然数中，最小的"呱呱数"是多少．
<result>31</result>