func_code_string: #include <bits/stdc++.h>   using namespace std;   bool sortbysec(const pair<int, int> a, const pair<int, int> b) {     return a.second < b.second;   }   int main() {     string s1;     cin >> s1;     string s2;     cin >> s2;     bool flag = false;     string ans =   0 ;     for (int i = 0; i < s1.length(); i++) {       if (int(s1[i]) < int(s2[i])) flag = true;     }     if (s1.length() != s2.length()) flag = true;     if (flag == false) {       for (int i = 0; i < s1.length(); i++) {         if (int(s1[i]) == int(s2[i]))           ans +=  z ;         else if (int(s1[i]) > int(s2[i]))           ans += s2[i];       }     }     if (flag == true)       cout <<  -1  << endl;     else       cout << ans << endl;     return 0;   }   