#include <bits/stdc++.h>
using namespace std;
const long long mx = 2e5 + 5;
long long n, base = 'a', arr[mx];
string s, t;
int main() {
  ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cin >> n >> s >> t;
  for (int i = n - 1; ~i; i--) {
    int j = i + 1;
    arr[j] += s[i] + t[i] - 2 * base;
    if (arr[j] >= 26) {
      arr[j] -= 26;
      arr[j - 1]++;
    }
  }
  for (int i = 0; i <= n; i++) {
    if (arr[i] & 1) {
      arr[i + 1] += 26;
    }
    arr[i] /= 2;
  }
  for (int i = 1; i <= n; i++) {
    cout << char(arr[i] + base);
  }
  return 0;
}
