#include<stdio.h>
int main()
{
    char s1[101],s2[101];
    int i,valid=1;
    scanf("%s%s",s1,s2);
    for(i=0;s1[i]!='0';i++){
        if(!((s1[i]>='A'&& s1[i]<='Z')||(s1[i]>='a'&&s1[i]<='z'))){
            valid=0;
        }
    }
    for(i=0;s2[i]!='0';i++){
         if(!((s2[i]>='A'&& s2[i]<='Z')||(s2[i]>='a'&&s2[i]<='z'))){
            valid=0;
        }
    }
    else if (valid==1){
        printf("%s%s",s1,s2);
    }
    else{
        printf("Invalid input");
    }
    return 0;
}