#include<stdio.h>
#include<string.h>
#include<ctype.h>
int Alpha(char s[]){
    for(int i=0;s[i]!='\0';i++){
        if(isalpha(s[i])){
            return 0;
        }
        return 1;
    }
}
int main(){
    char s1[];
    char s2[];
    scanf("%s%s",&s1[],&s2[]);
    if(Alpha(s1[])&&Alpha(s2[])){
        printf("%s",strcat(s1,s2));
    }
    else{
        printf("Invalid input");
    }
}