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 CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int maxn = 100000 + 5;
const int MOD = 1e9 + 7;
int f[maxn];
int main() {
  int n, t;
  string a, b, s;
  cin >> n >> t;
  cin >> a >> b;
  for (int i = 0; i < n; i++) {
    for (char c = 'a'; c <= 'z'; c++) {
      if (a[i] == c || b[i] == c) continue;
      s.push_back(c);
      break;
    }
  }
  int d1 = n - t, d2 = n - t;
  for (int i = 0; i < n; i++) {
    if (d1 == 0) break;
    if (a[i] == b[i]) {
      s[i] = a[i];
      d1--;
      d2--;
      f[i] = 1;
    }
  }
  for (int i = 0; i < n; i++) {
    if (f[i]) continue;
    if (d1) {
      d1--;
      s[i] = a[i];
      f[i] = 1;
    } else if (d2) {
      d2--;
      s[i] = b[i];
      f[i] = 1;
    }
  }
  if (!d1 && !d2)
    cout << s << endl;
  else
    cout << -1 << endl;
}