#include <bits/stdc++.h>
using namespace std;
int cnt[3], mp[5243][4];
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
//freopen("ws.INP", "r", stdin);
//freopen("ws.OUT", "w", stdout);
memset(cnt, 0, sizeof cnt);
memset(mp, 0, sizeof mp);
int n; cin >> n;
string a, b; cin >> a >> b;
for (int i = n - 1; i >= 0; i--) {
cnt[a[i] - 'a']++;
for (int j = 0; j < 3; j++)
mp[i][j] = mp[i + 1][j] + ((b[i] - 'a') == j);
} string res = "";
for (int i = 0; i < n; i++) {
for (int j = 0; j < 3; j++) {
if (!cnt[j] || (b[i] - 'a') == j) continue;
bool chk = true;
for (int c = 0; c < 3 && chk; c++) {
int tmp = 0;
for (int d = 0; d < 3; d++)
if (c != d) tmp += cnt[d] - (d == j);
if (mp[i + 1][c] > tmp) chk = false;
}
if (chk) {
res += (j + 'a');
cnt[j]--;
break;
}
}
} cout << res;
return 0;
}
/* In case of emergency,
___ _____ _____ _ _ ___
/ __|_ _\ \ / / __| | | | | _ \
| (_ || | \ V /| _| | |_| | _/
\___|___| \_/ |___| \___/|_|
*/
