// editor1121212
#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
char s1[100],s2[100];
int i, invalid = 0;
scanf("%s %s",s1,s2);
for(i + 0;s1[i]!=[i]'\0';i++){
    if(isdigit(s1[i])){
        invalid = 1;
        break;
    }
}
for (i=0; s2[i] !='\0';i++){
    if(isdigit(s2[i])){
          invalid = 1;
        break;
    }
}
if(invalid){
    printf("Invalid input");
}else{
    strcat(s1,s2);
    printf("%s",s1);
}
return 0;
}