Problem: 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.

Examples

Input

3 2
abc
xyc


Output

ayd

Input

1 0
c
b


Output

-1

Solution (in PYTHON3):

Solution:
n, t = map(int, input().split())
s1 = str(input())
s2 = str(input())
s1cnt, s2cnt = n - t, n - t
ans = [None] * n
# print(s1cnt, s2cnt)
for i in range(n):
    ch1, ch2 = s1[i], s2[i]
    if ch1 == ch2 and s1cnt and s2cnt:
        ans[i] = ch1
        s1cnt -= 1
        s2cnt -= 1
# print(ans)
for i in range(n):
    ch1, ch2 = s1[i], s2[i]
    if s1cnt and ans[i] == None:
        ans[i] = ch1
        s1cnt -= 1
    elif s2cnt and ans[i] == None:
        ans[i] = ch2
        s2cnt -= 1
    elif ans[i] == None:
        for j in range(ord('a'), ord('e')):
            if chr(j) != ch1 and chr(j) != ch2:
                ans[i] = chr(j)
                break

if s1cnt or s2cnt:
    print(-1)
else:
    print(''.join(ans))
# print(n,t, s1, s2)