Nightmare Brother

Your brother has a string $S$ of length $M$ with indices from $1$ to $M$. You want to know exactly what string $S$ is. To help you, he gives you $N$ hints that might help you to figure out $S$. Hint $i$ is represented by an integer $X_i$ and a string $T_i$, indicating that the string $T_i$ appears as a substring of $S$ starting from index $X_i$ of $S$. All the hints are unique, that is, there are no hints $i$ and $j$ such that $i \ne j$ while $X_i = X_j$ and $T_i = T_j$.

However, your brother is known to be mischievous and tells you that there might be at most one false hint among all $N$ hints he has given, but he didn’t tell you which.

A string $S$ is a possible solution if and only if there exists a set of at least $N - 1$ hints (that are assumed to be true) where string $S$ is the only string consistent with all of the hints in the set.

You would like to find a possible solution. If there is no possible solution, you should output -1. If there is more than one possible solution, you should output -2.

Input begins with two integers $N$ $M$ ($1 ≤ N ≤ 100$; $1 ≤ M ≤ 100$) representing the number of hints and the length of the scary string, respectively. Each of the next $N$ lines contains an integer and a string $X_i$ $T_i$ ($1 ≤ X_i , |T_i |$; $X_i + |T_i | - 1 ≤ M$) representing hint $i$. The string $T_i$ consists of only uppercase characters. It is guaranteed that there are no hints $i$ and $j$ such that $i \ne j$ while $X_i = X_j$ and $T_i = T_j$.

If there is exactly one possible solution as explained in the problem description above, then output the string $S$ in a single line. If there is no possible solution, then output -1 in a single line. If there is more than one possible solution, then output -2 in a single line.