#include<iostream>
#include<string>
#include<cctype>
using namespace std;

bool isValid(const string &s){
    if(s.empty()) return true;
    for(char c : s){
        if(!isalpha(c)) {
            return false;
        }
    }
    return true;
}
int main() {
    string word1, word2;
    if(!(cin>>word1)) return 0;
    if(!(cin>>word2)) return 0;
    if(!isValid(word1) || !isValid(word2)){
        cout<<"Invalid input"<<endl;
        return 0;
    }
    string merged =" "
    int i=0, j=0;
    int n1= word1.length();
    int n2= word2.length();
    while(i<n1 || j<n2){
        if(i<n1){
            merged+=word1[i++];
        }
        if(j<n2){
            merged+=word2[j++];
        }
    }
    cout<<merged<<endl;
    return 0;
}