Let's write digits in place of the letters $I, K, S$ so that the following subtraction is correct:

$K I S-$

SIK

$\overline{S K I}$
If we subtract $I$ from $I$, we should get 0, but when $K=0$, every digit would result in 0, so there must have been a remainder of 1 when subtracting the first digit, thus $K=9$. There is also a remainder of 1 when subtracting the second digits, so $S+(S+1)=K=9$; $S=4$, and thus from the subtraction of the first digits, $I=5$. Indeed, $954-459=495$.

Eisler Ottó (Bp.-i Cisztercita gimn. V. o.)