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 = input()
s2 = input()
p1 = n - t
p2 = n - t
s = [' ' for i in range(n)]
c = "abcdefghtyux"
for i in range(n):
    if(s1[i] == s2[i] and p1 > 0 and p2 > 0):
        s[i] = s1[i]
        p1 -= 1
        p2 -= 1
for i in range(n):
    if p1 > 0 and s[i] == ' ':
        p1 -= 1
        s[i] = s1[i]
    elif p2 > 0 and s[i] == ' ':
        p2 -= 1
        s[i] = s2[i]
if p1 == 0 and p2 == 0:
    for i in range(n):
        if s[i] == ' ':
            for x in range(len(c)):
                if(c[x] != s1[i] and c[x] != s2[i]):
                    s[i] = c[x]
                    break
    print(''.join(str(p) for p in s))
else: print("-1")