#include <bits/stdc++.h>   using namespace std;   int a[200005];   int b[200005];   int c[200005];   char str1[200005];   char str2[200005];   int main() {     int n;     while (scanf( %d , &n) != EOF) {       cin >> str1 >> str2;       int i;       for (i = 0; i < n; i++) {         a[i] = str1[i] -  a ;         b[i] = str2[i] -  a ;       }       for (i = n - 1; i >= 0; i--) {         if (b[i] >= a[i]) {           c[i] = b[i] - a[i];         } else {           c[i] = b[i] - a[i] + 26;           b[i - 1]--;         }       }       for (i = 0; i < n; i++) {         if (c[i] % 2 == 0) {           c[i] = c[i] / 2;         } else {           c[i] = c[i] / 2;           c[i + 1] += 26;         }       }       for (i = n - 1; i >= 0; i--) {         a[i] = a[i] + c[i];         while (a[i] >= 26) {           a[i] -= 26;           a[i - 1]++;         }       }       for (i = 0; i < n; i++) {         printf( %c , (char)(a[i] +  a ));       }       printf(  n );     }     return 0;   }   