func_code_string: #include <bits/stdc++.h>   using namespace std;   int n, t;   string str1, str2;   int main() {     scanf( %d %d , &n, &t);     cin >> str1 >> str2;     int l1 = n - t, l2 = n - t;     string ans;     ans.resize(n);     for (int i = 0; i < n; i++) {       if (l1 == 0 && l2 == 0) break;       if (str1[i] == str2[i]) {         ans[i] = str1[i];         l1--;         l2--;       }     }     if (l1 == 0 && l2 == 0) {       for (int i = 0; i < n; i++) {         if (ans[i] >=  a  && ans[i] <=  z ) continue;         for (int j =  a ; j <=  z ; j++) {           if (j != str1[i] && j != str2[i]) {             ans[i] = j;             break;           }         }       }     } else {       int state = 0;       for (int i = 0; i < n; i++) {         if (l1 == 0 && l2 == 0) {           if (ans[i] >=  a  && ans[i] <=  z ) continue;           for (int j =  a ; j <=  z ; j++) {             if (j != str1[i] && j != str2[i]) {               ans[i] = j;               break;             }           }         } else {           if (ans[i] >=  a  && ans[i] <=  z ) continue;           if (state == 0) {             l1--;             ans[i] = str1[i];             state = 1;           } else {             l2--;             ans[i] = str2[i];             state = 0;           }         }       }     }     if (l1 > 0 || l2 > 0)       printf( -1 n );     else       cout << ans << endl;   }   