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:
from sys import exit
n, m = map(int, input().split())
a = input()
b = input()
c = []
d = [0] * n
c = [i for i in range(n) if a[i] == b[i]]
l = len(c)
for i in range(min(l, n-m)):
    d[c[i]] = a[c[i]]
if l < n-m:
    u = n-m-l
    if l + u + u > n:
        print(-1)
        exit(0)
    else:
        u = n-m-l
        for i in range(n):
            if d[i] == 0 and u > 0:
                d[i] = a[i]
                u -= 1
                if u == 0: break
        u = n-m-l
        for i in range(n):
            if d[i] == 0 and u > 0:
                d[i] = b[i]
                u -= 1
                if u == 0: break
for i in range(n):
    if d[i] == 0:
        for e in ['a','b','c']:
            if e != a[i] and e != b[i]:
                print(e, end='')
                break
    else:
        print(d[i], end='')