#include <bits/stdc++.h>
using namespace std;
long long MOD = 1e9 + 7, MAX = 1e18;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long n, i;
  string second, r;
  cin >> n >> second >> r;
  vector<long long> a, b, c(n + 1, 0);
  a.push_back(0), b.push_back(0);
  for (auto i : second) a.push_back(i - 'a');
  for (auto i : r) b.push_back(i - 'a');
  for (i = n; i >= 0; i--) {
    c[i] = c[i] + a[i] + b[i];
    if (i && c[i] > 25) c[i] -= 26, c[i - 1]++;
  }
  string ans;
  for (i = 0; i <= n; i++) {
    if (i < n && (c[i] % 2)) c[i + 1] += 26;
    c[i] /= 2;
    if (i) ans.push_back('a' + c[i]);
  }
  cout << ans;
  return 0;
}
