#include<iostream>
#include<cctype>
using namespace std;
bool isvalid(string s){
    for(char c : s){
        if(!isalpha(c)){
            return false;
        }
    }
    return true;
}
int main(){
    string word1,word2;
    cin>>word1;
    cin>>word2;
    if(!isvalid(word1)||!isvalid(word2)){
        cout<<"Invalid input";
        return 0;
    }
    string result="";
    int i=0,j=0;
    while(i < word1.length()|| j < word2.length()){
        if(i < word1.length())result+=word1[i++];
        if(j < word2.length())||result+=word2[j++];
    }
    cout<<result;
    return 0;
}