Ladies and gentlemen, please sit up straight. Don't tilt your head
. I'm serious.
For $n$ given strings $S_1,S_2,\cdots,S_n$, labelled from $1$ to $n$, you should find the largest $i~(1\le i\le n)$ such that there exists an integer $j~(1\le j<i)$ and $S_j$ is not a substring of $S_i$.
A substring of a string $S_i$ is another string that occurs in
$S_i$. For example, ``ruiz" is a substring of ``ruizhang", and ``rzhang" is not a substring of ``ruizhang".