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Marina and Vasya

1000ms 262144K

Description:

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 s1, s2 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 s3 of length n, such that f(s1, s3) = f(s2, s3) = t. If there is no such string, print  - 1.

Input:

The first line contains two integers n and t (1 ≤ n ≤ 105, 0 ≤ t ≤ n).

The second line contains string s1 of length n, consisting of lowercase English letters.

The third line contain string s2 of length n, consisting of lowercase English letters.

Output:

Print a string of length n, differing from string s1 and from s2 in exactly t characters. Your string should consist only from lowercase English letters. If such string doesn't exist, print -1.

Sample Input:

3 2
abc
xyc

Sample Output:

ayd

Sample Input:

1 0
c
b

Sample Output:

-1

Informação

Codeforces

Provedor Codeforces

Código CF584C

Tags

constructive algorithmsgreedystrings

Submetido 0

BOUA! 0

Taxa de BOUA's 0%

Datas 09/05/2023 09:00:29

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