1007. From a natural number, the sum of its digits was subtracted, and from the resulting difference, the sum of its digits was subtracted again. If this process continues, with what number will the calculations end?
$\triangle$ The difference between a natural number and the sum of its digits is divisible by 9 (see supporting problem 120 from § 5), and this property is preserved at each step of the computation. But such a difference is non-negative and decreases with further continuation of the computations, so its last value is zero.

Answer: 0.