#include <bits/stdc++.h>   using namespace std;   void checkDefine();   string x;   string y;   string z;   int main() {     cin >> x >> y;     long long int n = x.size();     for (int i = (0), _b = (n - 1); i <= _b; i++) {       if (x[i] < y[i]) {         cout << -1;         return 0;       }     }     cout << y;     return 0;   }   void checkDefine() {     long long int n, a[200005];     map<long long int, long long int> m;     cin >> n;     for (int i = (0), _b = (n - 1); i <= _b; i++) {       cin >> a[i];       m[a[i]]++;     }     string s;     cin >> s;     {       cout <<  s             <<   =  ;       cout << (s) << endl;     };     {       cout <<  a             <<   =  ;       for (int _ = 0, _a = (n); _ < _a; _++) cout << a[_] <<    ;       cout << endl;     };     {       cout <<   ------------              <<   =  ;       cout << ( ------------ ) << endl;     };     for (__typeof(m.begin()) it = m.begin(); it != m.end(); ++it) {       cout << it->first <<     << it->second << endl;     }   }   