#include<iostream>
#include<cctype>
#include<string>
using namespace std;
 int main()
 {
    string a,b;
     if(!(cin>>a>>b))
    {
       cout<<"Invalid input"; 
    }
    else if(a.length()!=b.length())
     {
         cout<<"Invalid input"; 
    }
    else if(a.length()==b.length())
    {
        for(int i=0;i<a.length();i++)
        {
            if(a[i]==isdigit())
            {
                cout<<"Invalid input";
            }
        }
    }
    else if(a.length()==b.length())
    {
        for(int i=0;i<a.length();i++)
        {
            if(b[i]==isdigit())
            {
                cout<<"Invalid input";
            }
        }
    }
     else
     {
         for(int i=0;i<a.length();i++)
         {
          cout<<a[i]<<b[i]<<endl;
         }
     }
    return 0; 
}