#include<stdio.h>
#include<string.h>
int main(){
    char s1[40];
    char s2[40];
    char word;
    scanf("%s", a);
    scanf("%s", b);
    if('a'<=s1[40]&&'z'>=s1[40]||'A'<=s1[40]&&'Z'>=s1[40]||'a'<=s2[40]&&'z'>=s2[40]||'A'<=s2[40]&&'Z'>=s2[40]]{
        printf("%s",strcat(s1,s2));
    }
    else{
        printf("Invalid input");
    }
}