Unknown digit

Not long ago, the well-known slacker from previous Olympiads, student Khvostenko, graduated from university. Now, he is a respectable member of society—Stepan Andriyovych Khvostenko, postgraduate student under Professor Integralov. He is engaged in mathematics, computer science, robotics, conducts scientific research, and in his spare time, prepares the university team for programming competitions. Naturally, he needs to select talented and unorthodox thinkers for the team. For this, he presents them with various puzzles and problems to solve. At the latest selection, he offered the following challenge:

There are nine digits: 1, 2, 3, 4, 5, 6, 7, 8, 9. One digit is removed, and the remaining digits are arranged into several columns (from 1 to 8, inclusive). Then, all digits in each column are summed, and the results are written together, one after another, to form a number $K$.

Your task is: Given $K$, determine which digit was removed. Try to solve this problem yourself.

For example, if digit 4 was removed and the remaining digits were arranged arbitrarily into three columns:

The number $K$ would be: $71816$.