#include<iostream>
#include<string>
using namespace std;
int main()
{
    string word1, word2;
    cin>>word1>>word2;
    
for(int i=0;i<word1.length();i++){
    char c=word1[i];
    if(!((c>='a'&&c<='z')||(c>='A'&&c<='z'))){
        cout<<"Invalid input"<<endl;
        return 0;
    }
}
for(int i=0;i<word2.length();i++){
    char c=word2[i];
    if(!((c>='a'&&c<='z')||(c>='A'&&c<='z'))){
        cout<<"Invalid input"<<endl;
        return 0;
    }
}
int i=0;
while(i<word1.length()||i<word2.length){
    if(i<word1.length()){
        cout<<word1[i];
    }
    if(i<word2.length()){
        cout<<word2[i];
    }
    i=i+1;
}
cout<<endl;
return 0;


}