#include<iostream>
#include<string>
#include<cctype>
#include<algorithm>
using namespace std;
int main (){
    string W1,W2,res="";
    if (!(cin >> W1 >> W2)) return 0;
    for (int i=0;i<max(W1.size());++i)
    {if(i<W2.size()){
        
    } (!isalpha(static_cast<unsigned char>(W1[i])){
        cout<<"Invalid input";
        return 0;
    }
    res += W1[i];
}
if(i<n2){
    (!isalpha(static_cast<unsigned char>(W2[i])){
      cout<<"Invalid input";
     return 0;
         
     }
    res+=W2[i];
}
}
cout<<res<<endl;
return 0;
}