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.

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.

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.