#include <bits/stdc++.h>
using namespace std;
#define int long long
#define TL ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define rall(s) s.rbegin(),s.rend()
#define all(s) s.begin(),s.end()
#define pb push_back
#define sz(s) s.size()
#define se second
#define fi first
#define ll long long
#define ld long double
#define YES cout<<"YES\n"
#define Yes cout<<"Yes\n"
#define yes cout<<"yes\n"
#define NO cout<<"NO\n"
#define No cout<<"No\n"
#define no cout<<"no\n"
const int N = 1e6 + 9 , mod = 1e9 + 7;
const ll inf = 1e18;
const ll MOD = (ll)1e9+7;
void solve() {
ll n; cin >> n;
string res = "";
string a,b; cin >> a >> b;
map<char, ll> mp1;
map<char, ll> mp2;
for(ll i = 0;i<n;i++){
mp1[a[i]]++;
mp2[b[i]]++;
} //sort(all(a));
ll cnt = n;
for(ll i = 0;i<n;i++){
mp2[b[i]]--;
for(char ch : {'a', 'b', 'c'}) {
if(mp1[ch] > 0 && ch != b[i]) {
mp1[ch]--;
bool safe = true;
for(char k : {'a', 'b', 'c'}) {
if(mp1[k] + mp2[k] > cnt - 1) {
safe = false;
}
}
if(safe) {
res += ch;
break;
} else {
mp1[ch]++;
}
}
}
cnt--;
} cout << res << endl;
}
int32_t main(){
//freopen("kgraph.in", "r", stdin);
//freopen("kgraph.out", "w", stdout);
TL;
int test = 1; //cin>>test;
while(test--) solve();
}
