# include <iostream>
#include <string>
#include <cctype>
bool isValidWorld(const std::string& s){
    for (char count &c : s){
        if (!std::isalpha(c)){
            return false;
        }
    }
    return true;
}
int main(){
    std::string s1, s2;
    std::cin >> s1 >> s2;
    if (isValidWorld(s1) && isValidWorld(s2)){
        std::cout << s1 + s2 << std::end1;
    }else{
        std::cout << "Invalid input" << std::end1;
    }
    return 0;
}