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C. Marina and Vasya

time limit per test

1 secondmemory limit per test

256 megabytesinput

standard inputoutput

standard outputMarina 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.

Examples

Input

3 2

abc

xyc

Output

ayd

Input

1 0

c

b

Output

-1

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