#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a[200010], b[200010], c[200010];
  string s, t;
  ios::sync_with_stdio(false);
  memset(a, 0, sizeof(a));
  memset(b, 0, sizeof(b));
  memset(c, 0, sizeof(c));
  cin >> n >> s >> t;
  for (int i = 0; i < n; i++) {
    a[i] = s[i] - 'a';
    b[i] = t[i] - 'a';
  }
  for (int i = 0; i < n; i++) {
    c[i] = a[i] + b[i];
  }
  for (int i = 0; i < n; i++) {
    if (c[i] % 2) {
      c[i + 1] += 26;
    }
    c[i] /= 2;
  }
  for (int i = n - 1; i > 0; i--) {
    if (c[i] >= 26) {
      c[i] -= 26;
      c[i - 1]++;
    }
  }
  for (int i = 0; i < n; i++) {
    cout << (char)('a' + c[i]);
  }
  cout << endl;
  return 0;
}
