#include <bits/stdc++.h>   using namespace std;   int main() {     int a, b;     cin >> a >> b;     if (a > b) {       if (a == 9 && b == 1)         cout << 9 <<     << 10;       else         cout << -1;       return 0;     }     if ((b - a) > 1) {       cout << -1;       return 0;     }     if (b == a) {       cout << a << 98 <<     << b << 99;       return 0;     }     cout << a <<     << b;     return 0;   }   