#include <bits/stdc++.h>
using namespace std;
const int base = (int)('z' - 'a') + 1;
vector<int> sum(const vector<int>& a_, const vector<int>& b) {
  vector<int> a = a_;
  int carry = 0;
  for (size_t i = 0; i < max(a.size(), b.size()) || carry; ++i) {
    if (i == a.size()) a.push_back(0);
    a[i] += carry + (i < b.size() ? b[i] : 0);
    carry = a[i] >= base;
    if (carry) a[i] -= base;
  }
  return a;
}
vector<int> divv(const vector<int>& a_, int b) {
  vector<int> a = a_;
  int carry = 0;
  for (int i = (int)a.size() - 1; i >= 0; --i) {
    long long cur = a[i] + carry * 1ll * base;
    a[i] = int(cur / b);
    carry = int(cur % b);
  }
  while (a.size() > 1 && a.back() == 0) a.pop_back();
  return a;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  vector<int> a, b;
  int n;
  cin >> n;
  string as, bs;
  cin >> as >> bs;
  for (int i = n - 1; i >= 0; --i) {
    a.push_back(as[i] - 'a');
    b.push_back(bs[i] - 'a');
  }
  vector<int> c = sum(a, b);
  c = divv(c, 2);
  for (int i = n - 1; i >= 0; --i) {
    cout << (char)(c[i] + 'a');
  }
  cout << "\n";
}
