#include <bits/stdc++.h>
using namespace std;
const int maxn=2e5+10;
int a[maxn],n;
int main()
{
string b,c;
cin >> n >> b >>c;
for(int i=n-1;i>=0;i--)
{
a[i+1]+= int(c[i] - 'a') +int(b[i] - 'a');
a[i]=a[i]+a[i+1]/26;
a[i+1]%=26;
}
if(a[0]%2!=0) a[1]+=26;
for(int i=1;i<=n;i++)
{
cout<<char('a'+a[i]/2);
if(a[i] % 2 != 0) a[i+1]+=26;
}
return 0;
}