Marina loves strings of the same length and Vasya loves when there is a third string, different from them in exactly $*t*$ characters. Help Vasya find at least one such string.

More formally, you are given two strings $*s*_{1}$, $*s*_{2}$ of length $*n*$ and number $*t*$. Let's denote as $*f*(*a*, *b*)$ the number of characters in which strings $*a*$ and $*b*$ are different. Then your task will be to find any string $*s*_{3}$ of length $*n*$, such that $*f*(*s*_{1}, *s*_{3}) = *f*(*s*_{2}, *s*_{3}) = *t*$. If there is no such string, print $- 1$.

Input

The first line contains two integers $*n*$ and $*t*$ ($1 ≤ *n* ≤ 10^{5}$, $0 ≤ *t* ≤ *n*$).

The second line contains string $*s*_{1}$ of length $*n*$, consisting of lowercase English letters.

The third line contain string $*s*_{2}$ of length $*n*$, consisting of lowercase English letters.

Output

Print a string of length $*n*$, differing from string $*s*_{1}$ and from $*s*_{2}$ in exactly $*t*$ characters. Your string should consist only from lowercase English letters. If such string doesn't exist, print -1.