#include<stdio.h
#include<ctype.h>
#include<string.h>

int main(){
    char s1[101] , s2[102];
    
    scanf("%s", s1);
    scanf("s",s2);
    
    for (int i = 0; s1[i] != '\0'; i++) {
        if (!isalpha(s1[i])) {
            printf("Invalid input");
            return 0;
        }
    }
    
    for (int i = 0; s2[i] != '\0'; i++) {
        if (!isalpha(s2[i])) {
            printf("Invalid input");
        }
    }
    
    printf("%s%s", s1 , s2);
    
    return 0;
}