#include <stdio.h>
#include <algorithm>
#include <string>
#include <iostream>
int n, cnt1[3], cnt2[3];
std::string s, t, ans;
bool check(int i, int j)
{
cnt1[j]--, cnt2[t[i] - 'a']--;
for (int i = 0; i < 3; i++)
{
int sum = 0;
for (int j = 0; j < 3; j++)
if (i ^ j)
sum += cnt2[j];
if (cnt1[i] > sum)
return cnt1[j]++, cnt2[t[i] - 'a']++, false;
}
return true;
}
int main()
{
std::cin >> n >> s >> t;
for (int i = 0; i < n; i++)
cnt1[s[i] - 'a']++, cnt2[t[i] - 'a']++;
for (int i = 0; i < n; i++)
for (int j = 0; j < 3; j++)
if (cnt1[j] and j != t[i] - 'a' and check(i, j))
{
ans += j + 'a';
break;
}
return std::cout << ans, 0;
}
