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

int main() {
    string a, b, res = "";
    cin >> a >> b;
    
    for(char c:a) 
        if (isalpha(c)){
            cout << "Invalid input";
            return 0;
    }
    for(char c : b)
       if (isalpha(c)){
          cout << "Invalid input";
          return 0;
    }
    int i=0;
    while (i < a.size() &&i i < b.size())
          res += a[i++] + string(1, b[i++]);
    res += a.substr(i) + b.substr(i);
    
    cout << res;
}