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,k=map(int,input().split())
a=input()
b=input()
c=[]
ans=0
for i in range(n):
    if a[i]==b[i]:
        ans+=1
si=n-k
d=['a','b','c']
if ans>=si:
    for i in range(n):
        if a[i]==b[i] and si>0:
            c.append(a[i])
            si-=1
        else:
            ee=[a[i],b[i]]
            if 'a' not in ee:
                c.append('a')
            elif 'c' not in ee:
                c.append('c')
            else:
                c.append('b')
    print(''.join(c))
else:
    re1=si-ans
    re2=si-ans
    for i in range(n):
        if a[i]==b[i] :
            c.append(a[i])
        else:
            if re1>0:
                c.append(a[i])
                re1-=1
            elif re2>0:
                c.append(b[i])
                re2-=1
            else:
                ee=[a[i],b[i]]
                if 'a' not in ee:
                    c.append('a')
                elif 'c' not in ee:
                    c.append('c')
                else:
                    c.append('b')
                
            #print(re1,re2)
    if re1+re2==0:
        print(''.join(c))
    else:
        print(-1)