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

void main(void) {
	char x[1000] = "a";
	scanf("%s",x);
	char y[1000] = "a";
	scanf("%s",y);
	if((int)strlen(x) - (int)strlen(y) != 0 && (int)strlen(x) - (int)strlen(y) != 1){
		printf("?");
	}else{
		for(int i = 0 ; i < (int)strlen(x);i++){
			if(x[i] != '\0'){
				printf("%c",x[i]);
			}
			if(y[i] != '\0'){
				printf("%c",y[i]);
			}
		}
	}
}