#include <iostream>
using namespace std;
int main (){
    string a,b;
    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<b.size())
     cout<<a[i]<<b[i++];
    cout<<a.substr(i)<<b.substr(i);
}