#include <iostream>
#include <string>
using namespace std;

int main() {
    string s, t;
    cin >> s >> t;
    
    size_t k = 0;
    for (char c : s) {
        while (k < t.size()) {
            if (c == t[k]) break;
            ++k;
        }
    }
    
    if (k == t.size())
        cout << s << endl;
    else
        cout << -1 << endl;
    
    return 0;
}