#include <stdio.h>
#include <string.h>
#include <ctype.h>
int isAlphabetic(char str[]){
    for (int i = 0;str[i] != '\0';i++){
        if(!isalpha(str[i])){
            return 0;
        }
    }
    return 1;
}
int main(){
    char s1[101],s2[101];
    scanf("%s",s1);
    scanf("%s",s2);
    if(isAlphabetic(s1) && isAplhabetic(s2)){
        printf("%s%s",s1,s2);
    }else{
        printf("invalid input");
    } 
    return 0;
}