func_code_string: #include <bits/stdc++.h>   using namespace std;   const int INF = 2e9 + 10;   const int MOD = 1e9 + 7;   const int N = 1e6 + 10;   int n, k, m;   string x, y, z;   int main() {     ios_base::sync_with_stdio(0);     cout.tie(0);     cin.tie(0);     cin >> x >> y;     n = x.length();     int ans = 1;     for (int i = 0; i < n; i++) {       if (y[i] > x[i]) {         cout << -1;         return 0;       }       z += min(x[i], y[i]);     }     cout << z;     return 0;   }   