#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main(){
    string w1,w2,res="";
    if(!(cin>>w1>>w2))
return 0;
     int n1=w1.size();
     int n2=w2.size();
     int maxlength =max(n1,n2);
     for(int i=0;i<maxlength;++i){
         if(i<n1){
             if(!isalpha(static_cast<unsigned char>(w1[i]))){
                 cout<<"Inavlid input"<<endl;
                 return 0;
             }
             res+=w2[i];
         }
     }
     cout<<es<<endl;
     return 0;
}