Easy yet hard problem

If you browse Kattis, one of the most common solved problem is this Easiest Problem. At a glance the problem is easy. Given a number $N$, find the smallest digit $p > 10$ such that the digits sum of $p \cdot N$ is equal to the digits sum of $N$: $dsum(N) = dsum(p \cdot N)$. For example, when $N = 4$, there is such $p = 28$ such that $dsum(4 * 28 = 112) = dsum(4)$.

On pen and paper this problem is almost too easy to solve, just try all such $p$ by brute-force suffices. Yet this problem contains a few challenges fundamental to understanding of programming.

First, one needs to be able to convert a string into integer in his or her favourite programming language, a question that is popular enough on StackOverflow. Then convert that integer into a sequence of digits. A naive way is to take each character of the string and turn them into individual digits. Another way is to take modulus 10 and continue with division by 10. One also needs to write loops or recursions in order to brute-force for an answer.

Then, one also needs to know how to read and write stdio from their favourite programming language, which might be non trivial for starters.

Numerically easy problem might not be programmatically easy after all.