#include<stdio.h>
#include<string.h>
int main(){
    char s1[50],s2[50],username[50];
    scanf("%s",s1);
    scanf("%s",s2);
    for (int i=0;s1[i]!='0';i++){
        if(! isalpha(s1[i])){
            printf("Invalid input\n");
            return 0;
        }
    }
    for(int i=0;s2[i]!='0';i++){
        if(! isalpha(s2[i])){
            printf("Invalid input\n");
            return 0;
        }
    }
    strcpy(username,s1);
    strcat(username,s2);
    printf("%s\n",username);
}