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